MOTOROLA INC., 1992
MOTOROLA
MC68030
ENHANCED 32-BIT
MICROPROCESSOR
USER’S MANUAL
Third Edition
MOTOROLA
MC68030 USER’S MANUAL
xxiii
PREFACE
The
MC68030 User's Manual
describes the capabilities, operation, and programming of the
MC68030 32-bit second-generation enhanced microprocessor. The manual consists of the
following sections and appendix. For detailed information on the MC68030 instruction set
refer to M68000PM/AD,
M68000 Family Programmer's Reference Manual.
Section 1. Introduction
Section 2. Data Organization and Addressing Capabilities
Section 3. Instruction Set Summary
Section 4. Processing States
Section 5. Signal Description
Section 6. On-Chip Cache Memories
Section 7. Bus Operation
Section 8. Exception Processing
Section 9. Memory Management Unit
Section 10. Coprocessor Interface Description
Section 11. Instruction Execution Timing
Section 12. Applications Information
Section 13. Electrical Characteristics
Section 14. Ordering Information and Mechanical Data
Appendix A. M68000 Family Summary
Index
NOTE
In this manual, assertion and negation are used to specify forc-
ing a signal to a particular state. In particular, assertion and as-
sert refer to a signal that is active or true; negation and negate
indicate a signal that is inactive or false. These terms are used
independently of the voltage level (high or low) that they repre-
sent.
The audience of this manual includes systems designers, systems programmers, and
applications programmers. Systems designers need some knowledge of all sections, with
particular emphasis on Sections 1, 5, 6, 7, 13, 14, and Appendix A. Designers who
implement a coprocessor for their system also need a thorough knowledge of Section 10.
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Systems programmers should become familiar with Sections 1, 2, 3, 4, 6, 8, 9, 11, and
Appendix A. Applications programmers can find most of the information they need in
Sections 1, 2, 3, 4, 9, 11, 12, and Appendix A.
From a different viewpoint, the audience for this book consists of users of other M68000
Family members and those who are not familiar with these microprocessors. Users of the
other family members can find references to similarities to and differences from the other
Motorola microprocessors throughout the manual. However, Section 1 and Appendix A
specifically identify the MC68030 within the rest of the family and contrast its differences.
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TABLE OF CONTENTS
Paragraph
Number Title Page
Number
Section 1
Introduction
1.1 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3
1.2 MC68030 Extensions to the M68000 Family . . . . . . . . . . . . . . . . . . . 1-4
1.3 Programming Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
1.4 Data Types and Addressing Modes. . . . . . . . . . . . . . . . . . . . . . . . . . 1-10
1.5 Instruction Set Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-10
1.6 Virtual Memory and Virtual Machine Concepts . . . . . . . . . . . . . . . . . 1-12
1.6.1 Virtual Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-12
1.6.2 Virtual Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-14
1.7 The Memory Management Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-15
1.8 Pipelined Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-16
1.9 The Cache Memories. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-16
Section 2
Data Organization and Addressing Capabilities
2.1 Instruction Operands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
2.2 Organization of Data in Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
2.2.1 Data Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
2.2.2 Address Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
2.2.3 Control Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
2.3 Organization of Data in Memory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5
2.4 Addressing Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8
2.4.1 Data Register Direct Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9
2.4.2 Address Register Direct Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10
2.4.3 Address Register Indirect Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10
2.4.4 Address Register Indirect with Postincrement Mode. . . . . . . . . . . . 2-10
2.4.5 Address Register Indirect with Predecrement Mode. . . . . . . . . . . . 2-11
2.4.6 Address Register Indirect with Displacement Mode . . . . . . . . . . . . 2-12
2.4.7 Address Register Indirect with Index (8-Bit Displacement) Mode . . 2-12
2.4.8 Address Register Indirect with Index (Base Displacement) Mode. . 2-13
2.4.9 Memory Indirect Postindexed Mode . . . . . . . . . . . . . . . . . . . . . . . . 2-14
2.4.10 Memory Indirect Preindexed Mode . . . . . . . . . . . . . . . . . . . . . . . . . 2-15
2.4.11 Program Counter Indirect with Displacement Mode . . . . . . . . . . . . 2-16
2.4.12 Program Counter Indirect with Index (8-Bit Displacement) Mode . . 2-16
2.4.13 Program Counter Indirect with Index (Base Displacement) Mode. . 2-17
2.4.14 Program Counter Memory Indirect Postindexed Mode . . . . . . . . . . 2-18
2.4.15 Program Counter Memory Indirect Preindexed Mode. . . . . . . . . . . 2-19
2.4.16 Absolute Short Addressing Mode . . . . . . . . . . . . . . . . . . . . . . . . . . 2-20
2.4.17 Absolute Long Addressing Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . 2-20
2.4.18 Immediate Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21
2.5 Effective Address Encoding Summary. . . . . . . . . . . . . . . . . . . . . . . . 2-22
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2.6 Programmer`s View of Addressing Modes. . . . . . . . . . . . . . . . . . . . . 2-24
2.6.1 Addressing Capabilities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-25
2.6.2 General Addressing Mode Summary . . . . . . . . . . . . . . . . . . . . . . . 2-31
2.7 M68000 Family Addressing Compatibility . . . . . . . . . . . . . . . . . . . . . 2-36
2.8 Other Data Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-36
2.8.1 System Stack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-36
2.8.2 User Program Stacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-38
2.8.3 Queues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-39
Section 3
Instruction Set Summary
3.1 Instruction Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
3.2 Instruction Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
3.2.1 Data Movement Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4
3.2.2 Integer Arithmetic Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5
3.2.3 Logical Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
3.2.4 Shift and Rotate Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
3.2.5 Bit Manipulation Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8
3.2.6 Bit Field Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9
3.2.7 Binary–coded Decimal Instructions. . . . . . . . . . . . . . . . . . . . . . . . . 3-10
3.2.8 Program Control Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-11
3.2.9 System Control Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12
3.2.10 Memory Management Unit Instructions. . . . . . . . . . . . . . . . . . . . . . 3-13
3.2.11 Multiprocessor Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13
3.3 Integer Condition Codes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14
3.3.1 Condition Code Computation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-15
3.3.2 Conditional Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17
3.4 Instruction Set Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18
3.5 Instruction Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-25
3.5.1 Using the CAS and CAS2 Instructions . . . . . . . . . . . . . . . . . . . . . . 3-25
3.5.2 Nested Subroutine Calls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-30
3.5.3 Bit Field Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-31
3.5.4 Pipeline Synchronization with the Nop Instruction. . . . . . . . . . . . . . 3-32
Section 4
Processing States
4.1 Privilege Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2
4.1.1 Supervisor Privilege Level. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2
4.1.2 User Privilege Level. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3
4.1.3 Changing Privilege Level. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4
4.2 Address Space Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5
4.3 Exception Processing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6
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4.3.1 Exception Vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6
4.3.2 Exception Stack Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7
Section 5
Signal Description
5.1 Signal Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2
5.2 Function Code Signals (FC0–FC2) . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4
5.3 Address Bus (A0–A31). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4
5.4 Data Bus (D0–D31) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4
5.5 Transfer Size Signals (SIZ0, SIZ1). . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4
5.6 Bus Control Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5
5.6.1 Operand Cycle Start (OCS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5
5.6.2 External Cycle Start (ECS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5
5.6.3 Read/Write (R/W) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5
5.6.4 Read-Modify-Write Cycle (RMC). . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5
5.6.5 Address Strobe (AS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5
5.6.6 Data Strobe (DS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6
5.6.7 Data Buffer Enable (DBEN). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6
5.6.8 Data Transfer and Size Acknowledge (DSACK0, DSACK1). . . . . . 5-6
5.6.9 Synchronous Termination (STERM) . . . . . . . . . . . . . . . . . . . . . . . . 5-6
5.7 Cache Control Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7
5.7.1 Cache Inhibit Input (CIIN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7
5.7.2 Cache Inhibit Output (CIOUT). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7
5.7.3 Cache Burst Request (CBREQ) . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7
5.7.4 Cache Burst Acknowledge (CBACK). . . . . . . . . . . . . . . . . . . . . . . . 5-7
5.8 Interrupt Control Signals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8
5.8.1 Interrupt Priority Level Signals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8
5.8.2 Interrupt Pending (IPEND). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8
5.8.3 Autovector (AVEC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8
5.9 Bus Arbitration Control Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8
5.9.1 Bus Request (BR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8
5.9.2 Bus Grant (BG) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9
5.9.3 Bus Grant Acknowledge (BGACK) . . . . . . . . . . . . . . . . . . . . . . . . . 5-9
5.10 Bus Exception Control Signals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9
5.10.1 Reset (RESET) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9
5.10.2 Halt (HALT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9
5.10.3 Bus Error (BERR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9
5.11 Emulator Support Signals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10
5.11.1 Cache Disable (CDIS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10
5.11.2 MMU Disable (MMUDIS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10
5.11.3 Pipeline Refill (REFILL). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10
5.11.4 Internal Microsequencer Status (STATUS). . . . . . . . . . . . . . . . . . . 5-10
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5.12 Clock (CLK) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-11
5.13 Power Supply Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-11
5.14 Signal Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-11
Section 6
On-Chip Cache Memories
6.1 On-Chip Cache Organization and Operation . . . . . . . . . . . . . . . . . . . 6-3
6.1.1 Instruction Cache. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4
6.1.2 Data Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6
6.1.2.1 Write Allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8
6.1.2.2 Read-Modify-Write Accesses. . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-10
6.1.3 Cache Filling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-10
6.1.3.1 Single Entry Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-10
6.1.3.2 Burst Mode Filling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-15
6.2 Cache Reset. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-20
6.3 Cache Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-20
6.3.1 Cache Control Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-20
6.3.1.1 Write Allocate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-21
6.3.1.2 Data Burst Enable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-21
6.3.1.3 Clear Data Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-21
6.3.1.4 Clear Entry in Data Cache. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-21
6.3.1.5 Freeze Data Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-22
6.3.1.6 Enable Data Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-22
6.3.1.7 Instruction Burst Enable. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-22
6.3.1.8 Clear Instruction Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-22
6.3.1.9 Clear Entry in Instruction Cache . . . . . . . . . . . . . . . . . . . . . . . . . 6-22
6.3.1.10 Freeze Instruction Cache. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-23
6.3.1.11 Enable Instruction Cache. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-23
6.3.2 Cache Address Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-23
Section 7
Bus Operation
7.1 Bus Transfer Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1
7.1.1 Bus Control Signals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3
7.1.2 Address Bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4
7.1.3 Address Strobe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4
7.1.4 Data Bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5
7.1.5 Data Strobe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5
7.1.6 Data Buffer Enable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5
7.1.7 Bus Cycle Termination Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5
7.2 Data Transfer Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6
7.2.1 Dynamic Bus Sizing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6
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7.2.2 Misaligned Operands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13
7.2.3 Effects of Dynamic Bus Sizing and Operand Misalignment . . . . . . 7-19
7.2.4 Address, Size, and Data Bus Relationships . . . . . . . . . . . . . . . . . . 7-22
7.2.5 MC68030 versus MC68020 Dynamic Bus Sizing . . . . . . . . . . . . . . 7-24
7.2.6 Cache Filling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-24
7.2.7 Cache Interactions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-26
7.2.8 Asynchronous Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-27
7.2.9 Synchronous Operation with DSACKx . . . . . . . . . . . . . . . . . . . . . . 7-28
7.2.10 Synchronous Operation with STERM . . . . . . . . . . . . . . . . . . . . . . . 7-29
7.3 Data Transfer Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-30
7.3.1 Asynchronous Read Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-31
7.3.2 Asynchronous Write Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-37
7.3.3 Asynchronous Read-Modify-Write Cycle. . . . . . . . . . . . . . . . . . . . . 7-43
7.3.4 Synchronous Read Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-48
7.3.5 Synchronous Write Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-51
7.3.6 Synchronous Read-Modify-Write Cycle. . . . . . . . . . . . . . . . . . . . . . 7-54
7.3.7 Burst Operation Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-59
7.4 CPU Space Cycles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-68
7.4.1 Interrupt Acknowledge Bus Cycles . . . . . . . . . . . . . . . . . . . . . . . . . 7-69
7.4.1.1 Interrupt Acknowledge Cycle — Terminated Normally . . . . . . . . 7-70
7.4.1.2 Autovector Interrupt Acknowledge Cycle. . . . . . . . . . . . . . . . . . . 7-71
7.4.1.3 Spurious Interrupt Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-74
7.4.2 Breakpoint Acknowledge Cycle. . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-74
7.4.3 Coprocessor Communication Cycles . . . . . . . . . . . . . . . . . . . . . . . 7-74
7.5 Bus Exception Control Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-75
7.5.1 Bus Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-82
7.5.2 Retry Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-89
7.5.3 Halt Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-91
7.5.4 Double Bus Fault. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-94
7.6 Bus Synchronization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-95
7.7 Bus Arbitration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-96
7.7.1 Bus Request . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-98
7.7.2 Bus Grant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-99
7.7.3 Bus Grant Acknowledge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-100
7.7.4 Bus Arbitration Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-100
7.8 Reset Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-103
Section 8
Exception Processing
8.1 Exception Processing Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1
8.1.1 Reset Exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-5
8.1.2 Bus Error Exception. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-7
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8.1.3 Address Error Exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-8
8.1.4 Instruction Trap Exception. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-9
8.1.5 Illegal Instruction and Unimplemented Instruction Exceptions . . . . 8-9
8.1.6 Privilege Violation Exception. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-11
8.1.7 Trace Exception. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-12
8.1.8 Format Error Exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-14
8.1.9 Interrupt Exceptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-14
8.1.10 MMU Configuration Exception. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-21
8.1.11 Breakpoint Instruction Exception. . . . . . . . . . . . . . . . . . . . . . . . . . . 8-22
8.1.12 Multiple Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-23
8.1.13 Return from Exception. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-24
8.2 Bus Fault Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-27
8.2.1 Special Status Word (SSW) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-28
8.2.2 Using Software to Complete the Bus Cycles. . . . . . . . . . . . . . . . . . 8-29
8.2.3 Completing the Bus Cycles with Rte . . . . . . . . . . . . . . . . . . . . . . . . 8-31
8.3 Coprocessor Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-32
8.4 Exception Stack Frame Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-32
Section 9
Memory Management Unit
9.1 Translation Table Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-6
9.1.1 Translation Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8
9.1.2 Translation Table Descriptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10
9.2 Address Translation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-13
9.2.1 General Flow for Address Translation. . . . . . . . . . . . . . . . . . . . . . . 9-13
9.2.2 Effect of RESET On MMU. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-15
9.2.3 Effect of MMUDIS On Address Translation. . . . . . . . . . . . . . . . . . . 9-15
9.3 Transparent Translation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-16
9.4 Address Translation Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-17
9.5 Translation Table Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-20
9.5.1 Descriptor Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-20
9.5.1.1 Descriptor Field Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-20
9.5.1.2 Root Pointer Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-23
9.5.1.3 Short-Format Table Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . 9-24
9.5.1.4 Long-Fomat Table Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-24
9.5.1.5 Short-Format Early Termination Page Descriptor . . . . . . . . . . . . 9-25
9.5.1.6 Long-Format Early Termination Page Descriptor . . . . . . . . . . . . 9-25
9.5.1.7 Short-Format Page Descriptor. . . . . . . . . . . . . . . . . . . . . . . . . . . 9-26
9.5.1.8 Long-Format Page Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-26
9.5.1.9 Short-Format Invalid Descriptor. . . . . . . . . . . . . . . . . . . . . . . . . . 9-26
9.5.1.10 Long-Format Indirect Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . 9-27
9.5.1.11 Short-Format Indirect Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . 9-27
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9.5.1.12 Long-Format Indirect Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . 9-28
9.5.2 General Table Search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-28
9.5.3 Variations in Translation Table Structure . . . . . . . . . . . . . . . . . . . . 9-33
9.5.3.1 Early Termination and Contiguous Memory. . . . . . . . . . . . . . . . . 9-33
9.5.3.2 Indirection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-34
9.5.3.3 Table Sharing Between Tasks. . . . . . . . . . . . . . . . . . . . . . . . . . . 9-37
9.5.3.4 Paging of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-37
9.5.3.5 Dynamic Allocation of Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-40
9.5.4 Detail of Table Search Operations . . . . . . . . . . . . . . . . . . . . . . . . . 9-40
9.5.5 Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-43
9.5.5.1 Function Code Lookup. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-45
9.5.5.2 Supervisor Translation Tree. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-48
9.5.5.3 Supervisor Only . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-48
9.5.5.4 Write Protect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-48
9.6 MC68030 and MC68851 Mmu Differences . . . . . . . . . . . . . . . . . . . . 9-51
9.7 Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-52
9.7.1 Root Pointer Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-52
9.7.2 Translation Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-54
9.7.3 Transparent Translation Registers . . . . . . . . . . . . . . . . . . . . . . . . . 9-57
9.7.4 MMU Status Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-59
9.7.5 Register Programming Considerations . . . . . . . . . . . . . . . . . . . . . . 9-61
9.7.5.1 Register Side Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-61
9.7.5.2 MMU Status Register Decoding. . . . . . . . . . . . . . . . . . . . . . . . . . 9-61
9.7.5.3 MMU Configuration Exception. . . . . . . . . . . . . . . . . . . . . . . . . . . 9-62
9.8 Mmu Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-63
9.9 Defining and Using Page Tables in An Operating System. . . . . . . . . 9-65
9.9.1 Root Pointer Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-65
9.9.2 Task Memory Map Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-66
9.9.3 Impact of MMU Features On Table Definition. . . . . . . . . . . . . . . . . 9-68
9.9.3.1 Number of Table Levels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-68
9.9.3.2 Initial Shift Count . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-69
9.9.3.3 Limit Fields. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-70
9.9.3.4 Early Termination Page Descriptors . . . . . . . . . . . . . . . . . . . . . . 9-70
9.9.3.5 Indirect Descriptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-71
9.9.3.6 Using Unused Descriptor Bits . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-71
9.10 An Example of Paging Implementation in an Operating System . . . . 9-72
9.10.1 System Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-72
9.10.2 Allocation Routines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-78
9.10.3 Bus Error Handler Routine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-82
Section 10
Coprocessor Interface Description
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10.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1
10.1.1 Interface Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2
10.1.2 Concurrent Operation Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-3
10.1.3 Coprocessor Instruction Format . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-4
10.1.4 Coprocessor System Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-5
10.1.4.1 Coprocessor Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-5
10.1.4.2 Processor-Coprocessor Interface . . . . . . . . . . . . . . . . . . . . . . . . 10-6
10.1.4.3 Coprocessor Interface Register Selection. . . . . . . . . . . . . . . . . . 10-8
10.2 Coprocessor Instruction Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-9
10.2.1 Coprocessor General Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . 10-9
10.2.1.1 Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-10
10.2.1.2 Protocol.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-11
10.2.2 Coprocessor Conditional Instructions . . . . . . . . . . . . . . . . . . . . . . . 10-12
10.2.2.1 Branch On Coprocessor Condition Instruction. . . . . . . . . . . . . . . 10-13
10.2.2.1.1 Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-14
10.2.2.1.2 Protocol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-15
10.2.2.2 Set On Coprocessor Condition Instruction. . . . . . . . . . . . . . . . . . 10-15
10.2.2.2.1 Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-15
10.2.2.2.2 Protocol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-16
10.2.2.3 Test Coprocessor Condition, Decrement and Branch Instruction 10-17
10.2.2.3.1 Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-17
10.2.2.3.2 Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-18
10.2.2.4 Trap On Coprocessor Condition.. . . . . . . . . . . . . . . . . . . . . . . . . 10-18
10.2.2.4.1 Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-18
10.2.2.4.2 Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-19
10.2.3 Coprocessor Save and Restore Instructions. . . . . . . . . . . . . . . . . . 10-20
10.2.3.1 Coprocessor Internal State Frames. . . . . . . . . . . . . . . . . . . . . . . 10-20
10.2.3.2 Coprocessor Format Words. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-22
10.2.3.2.1 Empty/Reset Format Word.. . . . . . . . . . . . . . . . . . . . . . . . . . . 10-22
10.2.3.2.2 Not Ready Format Word.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-23
10.2.3.2.3 Invalid Format Word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-23
10.2.3.2.4 Valid Format Word. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-24
10.2.3.3 Coprocessor Context Save Instruction . . . . . . . . . . . . . . . . . . . . 10-24
10.2.3.3.1 Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-24
10.2.3.3.2 Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-25
10.2.3.4 Coprocessor Context Restore Instruction.. . . . . . . . . . . . . . . . . . 10-27
10.2.3.4.1 Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-27
10.2.3.4.2 Protocol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-28
10.3 Coprocessor Interface Register Set. . . . . . . . . . . . . . . . . . . . . . . . . . 10-29
10.3.1 Response CIR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-29
10.3.2 Control CIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-30
10.3.3 Save CIR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-30
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10.3.4 Restore CIR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-31
10.3.5 Operation Word CIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-31
10.3.6 Command CIR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-31
10.3.7 Condition CIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-31
10.3.8 Operand CIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-32
10.3.9 Register Select CIR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-32
10.3.10 Instruction Address CIR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-33
10.3.11 Operand Address CIR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-33
10.4 Coprocessor Response Primitives. . . . . . . . . . . . . . . . . . . . . . . . . . . 10-33
10.4.1 ScanPC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-34
10.4.2 Coprocessor Response Primitive General Format . . . . . . . . . . . . . 10-35
10.4.3 Busy Primitive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-36
10.4.4 Null Primitive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-37
10.4.5 Supervisor Check Primitive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-40
10.4.6 Transfer Operation Word Primitive . . . . . . . . . . . . . . . . . . . . . . . . . 10-40
10.4.7 Transfer from Instruction Stream Primitive . . . . . . . . . . . . . . . . . . . 10-41
10.4.8 Evaluate and Transfer Effective Address Primitive . . . . . . . . . . . . . 10-42
10.4.9 Evaluate Effective Address and Transfer Data Primitive. . . . . . . . . 10-43
10.4.10 Write to Previously Evaluated Effective Address Primitive . . . . . . . 10-46
10.4.11 Take Address and Transfer Data Primitive . . . . . . . . . . . . . . . . . . . 10-48
10.4.12 Transfer to/from Top of Stack Primitive. . . . . . . . . . . . . . . . . . . . . . 10-49
10.4.13 Transfer Single Main Processor Register Primitive. . . . . . . . . . . . . 10-50
10.4.14 Transfer Main Processor Control Register Primitive . . . . . . . . . . . . 10-50
10.4.15 Transfer Multiple Main Processor Registers Primitive. . . . . . . . . . . 10-52
10.4.16 Transfer Multiple Coprocessor Registers Primitive . . . . . . . . . . . . . 10-52
10.4.17 Transfer Status Register and ScanPC Primitive . . . . . . . . . . . . . . . 10-55
10.4.18 Take Pre-Instruction Exception Primitive. . . . . . . . . . . . . . . . . . . . . 10-56
10.4.19 Take Mid-Instruction Exception Primitive . . . . . . . . . . . . . . . . . . . . 10-58
10.4.20 Take Post-Instruction Exception Primitive. . . . . . . . . . . . . . . . . . . . 10-60
10.5 Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-61
10.5.1 Coprocessor-Detected Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . 10-61
10.5.1.1 Coprocessor-Detected Protocol Violations . . . . . . . . . . . . . . . . . 10-62
10.5.1.2 Coprocessor-Detected Illegal Command or Condition Words. . . 10-63
10.5.1.3 Coprocessor Data-Processing Exceptions . . . . . . . . . . . . . . . . . 10-63
10.5.1.4 Coprocessor System-Related Exceptions . . . . . . . . . . . . . . . . . . 10-64
10.5.1.5 Format Errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-64
10.5.2 Main-Processor-Detected Exceptions. . . . . . . . . . . . . . . . . . . . . . . 10-65
10.5.2.1 Protocol Violations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-65
10.5.2.2 F-Line Emulator Exceptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-68
10.5.2.3 Privilege Violations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-69
10.5.2.4 cpTRAPcc Instruction Traps . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-69
10.5.2.5 Trace Exceptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-70
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10.5.2.6 Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-71
10.5.2.7 Format Errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-71
10.5.2.8 Address and Bus Errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-72
10.5.3 Coprocessor Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-72
10.6 Coprocessor Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-72
Section 11
Instruction Execution Timing
11.1 Performance Tradeoffs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1
11.2 Resource Scheduling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2
11.2.1 Microsequencer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2
11.2.2 Instruction Pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2
11.2.3 Instruction Cache. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-4
11.2.4 Data Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-4
11.2.5 Bus Controller Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-4
11.2.5.1 Instruction Fetch Pending Buffer . . . . . . . . . . . . . . . . . . . . . . . . . 11-5
11.2.5.2 Write Pending Buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-5
11.2.5.3 Micro Bus Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-5
11.2.6 Memory Management Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-6
11.3 Instruction Execution Timing Calculations . . . . . . . . . . . . . . . . . . . . . 11-6
11.3.1 Instruction-Cache Case. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-6
11.3.2 Overlap and Best Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-7
11.3.3 Average No-Cache Case. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-8
11.3.4 Actual Instruction-Cache-Case Execution Time Calculations . . . . . 11-11
11.4 Effect of Data Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-16
11.5 Effect of Wait States. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-18
11.6 Instruction Timing Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-24
11.6.1 Fetch Effective Address (fea) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-26
11.6.2 Fetch Immediate Effective Address (fiea) . . . . . . . . . . . . . . . . . . . . 11-28
11.6.3 Calculate Effective Address (cea) . . . . . . . . . . . . . . . . . . . . . . . . . . 11-30
11.6.4 Calculate Immediate Effective Address (ciea). . . . . . . . . . . . . . . . . 11-32
11.6.5 Jump Effective Address. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-35
11.6.6 MOVE Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-37
11.6.7 Special-Purpose Move Instruction. . . . . . . . . . . . . . . . . . . . . . . . . . 11-39
11.6.8 Arithmetical/Logical Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-40
11.6.9 Immediate Arithmetical/Logical Instructions . . . . . . . . . . . . . . . . . . 11-42
11.6.10 Binary-Coded Decimal and Extended Instructions . . . . . . . . . . . . . 11-43
11.6.11 Single Operand Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-44
11.6.12 Shift/Rotate Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-45
11.6.13 Bit Manipulation Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-46
11.6.14 Bit Field Manipulation Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . 11-47
11.6.15 Conditional Branch Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-48
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11.6.16 Control Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-49
11.6.17 Exception-Related Instructions and Operations . . . . . . . . . . . . . . . 11-50
11.6.18 Save and Restore Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-51
11.7 Address Translation Tree Search Timing. . . . . . . . . . . . . . . . . . . . . . 11-51
11.7.1 MMU Effective Address Calculation . . . . . . . . . . . . . . . . . . . . . . . . 11-58
11.7.2 MMU Instruction Timing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-60
11.8 Interrupt Latency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-61
11.9 Bus Arbitration Latency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-62
Section 12
Applications Information
12.1 Adapting the MC68030 to MC68020 Designs . . . . . . . . . . . . . . . . . . 12-1
12.1.1 Signal Routing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-2
12.1.2 Hardware Differences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-3
12.1.3 Software Differences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-4
12.2 Floating-Point Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-5
12.3 Byte Select Logic for the MC68030 . . . . . . . . . . . . . . . . . . . . . . . . . . 12-9
12.4 Memory Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-11
12.4.1 Access Time Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-14
12.4.2 Burst Mode Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-17
12.5 Static RAM Memory Banks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-18
12.5.1 A Two-Clock Synchronous Memory Bank Using SRAMS. . . . . . . . 12-18
12.5.2 A 2-1-1-1 Burst Mode Memory Bank Using SRAMS. . . . . . . . . . . . 12-24
12.5.3 A 3-1-1-1 Burst Mode Memory Bank Using SRAMS. . . . . . . . . . . . 12-27
12.6 External Caches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-30
12.6.1 Cache Implementation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-32
12.6.2 Instruction-Only External Cache Implementations . . . . . . . . . . . . . 12-35
12.7 Debugging Aids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-35
12.7.1 Status and Refill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-36
12.7.2 Real-Time Instruction Trace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-39
12.8 Power and Ground Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . 12-43
Section 13
Electrical Characteristics
13.1 Maximum Ratings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-1
13.2 Thermal Characteristics — PGA Package. . . . . . . . . . . . . . . . . . . . . 13-1
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Section 14
Ordering Information
and Mechanical Data
14.1 Standard MC68030 Ordering Information . . . . . . . . . . . . . . . . . . . . . 14-1
14.2 Pin Assignments — Pin Grid Array (RC Suffix) . . . . . . . . . . . . . . . . . 14-2
14.3 Pin Assignments — Ceramic Surface Mount (FE Suffix). . . . . . . . . . 14-3
14.4 Package Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-4
Appendix A
M68000 Family Summary
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LIST OF ILLUSTRATIONS
Figure
Number Title Page
Number
1-1 Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2
1-2 User Programming Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
1-3 Supervisor Programming Model Supplement. . . . . . . . . . . . . . . . . . . . . . . 1-7
1-4 Status Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8
2-1 Memory Operand Address. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6
2-2 Memory Data Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7
2-3 Single Effective Address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8
2-4 Effective Address Specification Formats . . . . . . . . . . . . . . . . . . . . . . . . . . 2-23
2-5 Using SIZE in the Index Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-25
2-6 Using Absolute Address with Indexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-26
2-7 Addressing Array Items . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-27
2-8 Using Indirect Absolute Memory Addressing . . . . . . . . . . . . . . . . . . . . . . . 2-28
2-9 Accessing an Item in a Structure Using a Pointer . . . . . . . . . . . . . . . . . . . 2-28
2-10 Indirect Addressing, Suppressed Index Register. . . . . . . . . . . . . . . . . . . . 2-29
2-11 Preindexed Indirect Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-29
2-12 Postindexed Indirect Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-30
2-13 Preindexed Indirect Addressing with Outer Displacement. . . . . . . . . . . . . 2-30
2-14 Postindexed Indirect Addressing with Outer Displacement . . . . . . . . . . . . 2-31
2-15 M68000 Family Address Extension Words . . . . . . . . . . . . . . . . . . . . . . . . 2-37
3-1 Instruction Word General Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
3-2 Linked List Insertion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-26
3-3 Linked List Deletion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-27
3-4 Doubly Linked List Insertion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-29
3-5 Doubly Linked List Deletion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-30
4-1 General Exception Stack Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7
5-1 Functional Signal Groups. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
6-1 Internal Caches and the MC68030. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2
6-2 On-Chip Instruction Cache Organization . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5
6-3 On-Chip Data Cache Organization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7
6-4 No-Write-Allocation and Write-Allocation Mode Examples . . . . . . . . . . . . 6-9
6-5 Single Entry Mode Operation — 8-Bit Port . . . . . . . . . . . . . . . . . . . . . . . . 6-11
6-6 Single Entry Mode Operation — 16-Bit Port . . . . . . . . . . . . . . . . . . . . . . . 6-12
6-7 Single Entry Mode Operation — 32-Bit Port . . . . . . . . . . . . . . . . . . . . . . . 6-12
6-8 Single Entry Mode Operation — Misaligned Long Word and 8-Bit Port. . . 6-13
6-9 Single Entry Mode Operation — Misaligned Long Word and 16-Bit Port. . 6-14
6-10 Single Entry Mode Operation — Misaligned Long Word and 32-Bit
DSACKx Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-15
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Figure
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6-11 Burst Operation Cycles and Burst Mode . . . . . . . . . . . . . . . . . . . . . . . . . . 6-17
6-12 Burst Filling Wraparound Example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-17
6-13 Deferred Burst Filling Example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-18
6-14 Cache Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-21
6-15 Cache Address Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-23
7-1 Relationship between External and Internal Signals . . . . . . . . . . . . . . . . . 7-2
7-2 Asynchronous Input Sample Window. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3
7-3 Internal Operand Representation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-8
7-4 MC68030 Interface to Various Port Sizes . . . . . . . . . . . . . . . . . . . . . . . . . 7-9
7-5 Example of Long-Word Transfer to Word Port. . . . . . . . . . . . . . . . . . . . . . 7-11
7-6 Long-Word Operand Write Timing (16-Bit Data Port) . . . . . . . . . . . . . . . . 7-12
7-7 Example of Word Transfer to Byte Port . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13
7-8 Word Operand Write Timing (8-Bit Data Port) . . . . . . . . . . . . . . . . . . . . . . 7-14
7-9 Misaligned Long-Word Transfer to Word Port Example. . . . . . . . . . . . . . . 7-15
7-10 Misaligned Long-Word Transfer to Word Port . . . . . . . . . . . . . . . . . . . . . . 7-16
7-11 Misaligned Cachable Long-Word Transfer from Word Port Example . . . . 7-17
7-12 Misaligned Word Transfer to Word Port Example . . . . . . . . . . . . . . . . . . . 7-17
7-13 Misaligned Word Transfer to Word Port. . . . . . . . . . . . . . . . . . . . . . . . . . . 7-18
7-14 Example of Misaligned Cachable Word Transfer from Word Bus . . . . . . . 7-20
7-15 Misaligned Long-Word Transfer to Long-Word Port. . . . . . . . . . . . . . . . . . 7-20
7-16 Misaligned Write Cycles to Long-Word Port. . . . . . . . . . . . . . . . . . . . . . . . 7-21
7-17 Misaligned Cachable Long-Word Transfer from Long-Word Bus. . . . . . . . 7-22
7-18 Byte Data Select Generation for 16- and 32-Bit Ports . . . . . . . . . . . . . . . . 7-25
7-19 Asynchronous Long-Word Read Cycle Flowchart . . . . . . . . . . . . . . . . . . . 7-32
7-20 Asynchronous Byte Read Cycle Flowchart . . . . . . . . . . . . . . . . . . . . . . . . 7-32
7-21 Asynchronous Byte and Word Read Cycles — 32-Bit Port . . . . . . . . . . . . 7-33
7-22 Long-Word Read — 8-Bit Port with CIOUT Asserted. . . . . . . . . . . . . . . . . 7-34
7-23 Long-Word Read — 16-Bit and 32-Bit Port . . . . . . . . . . . . . . . . . . . . . . . . 7-35
7-24 Asynchronous Write Cycle Flowchart. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-37
7-25 Asynchronous Read-Write-Read Cycles — 32-Bit Port. . . . . . . . . . . . . . . 7-38
7-26 Asynchronous Byte and Word Write Cycles — 32-Bit Port . . . . . . . . . . . . 7-39
7-27 Long-Word Operand Write — 8-Bit Port. . . . . . . . . . . . . . . . . . . . . . . . . . . 7-40
7-28 Long-Word Operand Write — 16-Bit Port. . . . . . . . . . . . . . . . . . . . . . . . . . 7-41
7-29 Asynchronous Read-Modify-Write Cycle Flowchart. . . . . . . . . . . . . . . . . . 7-44
7-30 Asynchronous Byte Read-Modify-Write Cycle — 32-Bit Port
(TAS Instruction with CIOUT or CIIN Asserted). . . . . . . . . . . . . . . . . . . . . 7-45
7-31 Synchronous Long-Word Read Cycle Flowchart —
No Burst Allowed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-49
7-32 Synchronous Read with CIIN Asserted and CBACK Negated. . . . . . . . . . 7-50
7-33 Synchronous Write Cycle Flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-52
7-34 Synchronous Write Cycle with Wait States — CIOUT Asserted . . . . . . . . 7-53
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Figure
Number Title Page
Number
LIST OF ILLUSTRATIONS (Continued)
7-35 Synchronous Read-Modify-Write Cycle Flowchart. . . . . . . . . . . . . . . . . . . 7-55
7-36 Synchronous Read-Modify-Write Cycle Timing — CIIN Asserted . . . . . . . 7-56
7-37 Burst Operation Flowchart — Four Long Words Transferred. . . . . . . . . . . 7-62
7-38 Long-Word Operand Request from $07 with
Burst Request and Wait Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-63
7-39 Long-Word Operand Request from $07 with
Burst Request — CBACK Negated Early. . . . . . . . . . . . . . . . . . . . . . . . . . 7-64
7-40 Long-Word Operand Request from $0E — Burst Fill Deferred . . . . . . . . . 7-65
7-41 Long-Word Operand Request from $07 with
Burst Request — CBACK and CIIN Asserted . . . . . . . . . . . . . . . . . . . . . . 7-66
7-42 MC68030 CPU Space Address Encoding . . . . . . . . . . . . . . . . . . . . . . . . . 7-69
7-43 Interrupt Acknowledge Cycle Flowchart. . . . . . . . . . . . . . . . . . . . . . . . . . . 7-71
7-44 Interrupt Acknowledge Cycle Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-72
7-45 Autovector Operation Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-73
7-46 Breakpoint Operation Flow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-75
7-47 Breakpoint Acknowledge Cycle Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-76
7-48 Breakpoint Acknowledge Cycle Timing (Exception Signaled) . . . . . . . . . . 7-77
7-49 Bus Error without DSACKx. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-84
7-50 Late Bus Error with DSACKx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-85
7-51 Late Bus Error with STERM — Exception Taken. . . . . . . . . . . . . . . . . . . . 7-86
7-52 Long-Word Operand Request — Late BERR on Third Access . . . . . . . . . 7-87
7-53 Long-Word Operand Request — BERR on Second Access . . . . . . . . . . . 7-88
7-54 Asynchronous Late Retry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-90
7-55 Synchronous Late Retry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-91
7-56 Late Retry Operation for a Burst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-92
7-57 Halt Operation Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-93
7-58 Bus Synchronization Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-96
7-59 Bus Arbitration Flowchart for Single Request. . . . . . . . . . . . . . . . . . . . . . . 7-98
7-60 Bus Arbitration Operation Timing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-99
7-61 Bus Arbitration State Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-101
7-62 Single-Wire Bus Arbitration Timing Diagram . . . . . . . . . . . . . . . . . . . . . . . 7-103
7-63 Bus Arbitration Operation (Bus Inactive) . . . . . . . . . . . . . . . . . . . . . . . . . . 7-104
7-64 Initial Reset Operation Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-105
7-65 Processor-Generated Reset Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-106
8-1 Reset Operation Flowchart. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-6
8-2 Interrupt Pending Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-15
8-3 Interrupt Recognition Examples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-17
8-4 Assertion of IPEND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-18
8-5 Interrupt Exception Processing Flowchart . . . . . . . . . . . . . . . . . . . . . . . . . 8-19
8-6 Examples of Interrupt Recognition and Instruction Boundaries . . . . . . . . . 8-20
8-7 Breakpoint Instruction Flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-23
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MOTOROLA
LIST OF ILLUSTRATIONS (Continued)
Figure
Number Title Page
Number
8-8 RTE Instruction for Throwaway Four-Word Frame . . . . . . . . . . . . . . . . . . 8-26
8-9 Special Status Word (SSW). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-28
9-1 MMU Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-3
9-2 MMU Programming Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-4
9-3 Translation Table Tree. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5
9-4 Example Translation Table Tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-7
9-5 Example Translation Tree Layout in Memory. . . . . . . . . . . . . . . . . . . . . . . 9-8
9-6 Derivation of Table Index Fields. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-9
9-7 Example Translation Tree Using Different Format Descriptors . . . . . . . . . 9-12
9-8 Address Translation General Flowchart. . . . . . . . . . . . . . . . . . . . . . . . . . . 9-14
9-9 Root Pointer Descriptor Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-23
9-10 Short-Format Table Descriptor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-24
9-11 Long-Format Table Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-24
9-12 Short-Format Page Descriptor and Short-Format Early
Termination Page Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-25
9-13 Long-Format Early Termination Page Descriptor. . . . . . . . . . . . . . . . . . . . 9-25
9-14 Long-Format Page Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-26
9-15 Short-Format Invalid Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-26
9-16 Long-Format Invalid Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-27
9-17 Short-Format Indirect Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-27
9-18 Long-Format Indirect Descriptor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-28
9-19 Simplified Table Search Flowchart. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-29
9-20 Five-Level Table Search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-31
9-21 Example Translation Tree Using Contiguous Memory. . . . . . . . . . . . . . . . 9-35
9-22 Example Translation Tree Using Indirect Descriptors . . . . . . . . . . . . . . . . 9-36
9-23 Example Translation Tree Using Shared Tables . . . . . . . . . . . . . . . . . . . . 9-38
9-24 Example Translation Tree with Nonresident Tables. . . . . . . . . . . . . . . . . . 9-39
9-25 Detailed Flowchart of MMU Table Search Operation. . . . . . . . . . . . . . . . . 9-41
9-26 Table Search Initialization Flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-42
9-27 ATC Entry Creation Flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-42
9-28 Limit Check Procedure Flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-43
9-29 Detailed Flowchart of Descriptor Fetch Operation . . . . . . . . . . . . . . . . . . . 9-44
9-30 Logical Address Map Using Function Code Lookup . . . . . . . . . . . . . . . . . 9-45
9-31 Example Translation Tree Using Function Code Lookup. . . . . . . . . . . . . . 9-46
9-32 Example Translation Tree Structure for Two Tasks. . . . . . . . . . . . . . . . . . 9-47
9-33 Exmple Logical Address Map with Shared Supervisor
and User Address Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-49
9-34 Exmple Translation Tree Using S and WP Bits to Set Protection . . . . . . . 9-50
9-35 Root Pointer Register (CRP, SRP) Format . . . . . . . . . . . . . . . . . . . . . . . . 9-54
9-36 Translation Control Register (TC) Format . . . . . . . . . . . . . . . . . . . . . . . . . 9-54
9-37 Transparent Translation Register (TT0 and TT1) Format . . . . . . . . . . . . . 9-57
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Figure
Number Title Page
Number
LIST OF ILLUSTRATIONS (Continued)
9-38 MMU Status Register (MMUSR) Format . . . . . . . . . . . . . . . . . . . . . . . . . . 9-59
9-39 MMU Status Interpretation PTEST Level 0 . . . . . . . . . . . . . . . . . . . . . . . . 9-62
9-40 MMU Status Interpretation PTEST Level 7 . . . . . . . . . . . . . . . . . . . . . . . . 9-63
10-1 F-Line Coprocessor Instruction Operation Word . . . . . . . . . . . . . . . . . . . . 10-4
10-2 Asynchronous Non-DMA M68000 Coprocessor Interface Signal Usage. . 10-6
10-3 MC68030 CPU Space Address Encodings . . . . . . . . . . . . . . . . . . . . . . . . 10-7
10-4 Coprocessor Address Map in MC68030 CPU Space. . . . . . . . . . . . . . . . . 10-8
10-5 Coprocessor Interface Register Set Map. . . . . . . . . . . . . . . . . . . . . . . . . . 10-9
10-6 Coprocessor General Instruction Format (cpGEN) . . . . . . . . . . . . . . . . . . 10-10
10-7 Coprocessor Interface Protocol for General Category Instructions . . . . . . 10-11
10-8 Coprocessor Interface Protocol for Conditional Category Instructions. . . . 10-13
10-9 Branch on Coprocessor Condition Instruction (cpBcc.W) . . . . . . . . . . . . . 10-14
10-10 Branch On Coprocessor Condition Instruction (cpBcc.L). . . . . . . . . . . . . . 10-14
10-11 Set On Coprocessor Condition (cpScc) . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-15
10-12 Test Coprocessor Condition, Decrement and Branch
Instruction Format (cpDBcc). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-17
10-13 Trap On Coprocessor Condition (cpTRAPcc) . . . . . . . . . . . . . . . . . . . . . . 10-18
10-14 Coprocessor State Frame Format in Memory . . . . . . . . . . . . . . . . . . . . . . 10-21
10-15 Coprocessor Context Save Instruction Format (cpSAVE) . . . . . . . . . . . . . 10-25
10-16 Coprocessor Context Save Instruction Protocol. . . . . . . . . . . . . . . . . . . . . 10-26
10-17 Coprocessor Context Restore Instruction Format (cpRESTORE) . . . . . . . 10-27
10-18 Coprocessor Context Restore Instruction Protocol . . . . . . . . . . . . . . . . . . 10-28
10-19 Control CIR Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-30
10-20 Condition CIR Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-31
10-21 Operand Alignment for Operand CIR Accesses. . . . . . . . . . . . . . . . . . . . . 10-32
10-22 Coprocessor Response Primitive Format. . . . . . . . . . . . . . . . . . . . . . . . . . 10-35
10-23 Busy Primitive Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-36
10-24 Null Primitive Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-37
10-25 Supervisor Check Primitive Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-40
10-26 Transfer Operation Word Primitive Format . . . . . . . . . . . . . . . . . . . . . . . . 10-41
10-27 Transfer from Instruction Stream Primitive Format . . . . . . . . . . . . . . . . . . 10-41
10-28 Evaluate and Transfer Effective Address Primitive Format . . . . . . . . . . . . 10-42
10-29 Evaluate Effective Address and Transfer Data Primitive . . . . . . . . . . . . . . 10-43
10-30 Write to Previously Evaluated EffectiveAddress Primitive Format. . . . . . . 10-46
10-31 Take Address and Transfer Data Primitive Format . . . . . . . . . . . . . . . . . . 10-48
10-32 Transfer To/From Top of Stack Primitive Format. . . . . . . . . . . . . . . . . . . . 10-49
10-33 Transfer Single Main Processor Register Primitive Format . . . . . . . . . . . . 10-50
10-34 Transfer Main Processor Control Register Primitive Format . . . . . . . . . . . 10-51
10-35 Transfer Multiple Main Processor Registers Primitive Format. . . . . . . . . . 10-52
10-36 Register Select Mask Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-52
10-37 Transfer Multiple Coprocessor Registers Primitive Format . . . . . . . . . . . . 10-53
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MC68030 USER’S MANUAL
MOTOROLA
LIST OF ILLUSTRATIONS (Concluded)
Figure
Number Title Page
Number
10-38 Operand Format in Memory for Transfer to —(An) . . . . . . . . . . . . . . . . . . 10-54
10-39 Transfer Status Register and ScanPC Primitive Format . . . . . . . . . . . . . . 10-55
10-40 Take Pre-Instruction Exception Primitive Format. . . . . . . . . . . . . . . . . . . . 10-56
10-41 MC68030 Pre-Instruction Stack Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-57
10-42 Take Mid-Instruction Exception Primitive Format. . . . . . . . . . . . . . . . . . . . 10-58
10-43 MC68030 Mid-Instruction Stack Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-59
10-44 Take Post-Instruction Exception Primitive Format . . . . . . . . . . . . . . . . . . . 10-60
10-45 MC68030 Post-Instruction Stack Frame . . . . . . . . . . . . . . . . . . . . . . . . . . 10-60
11-1 Block Diagram – Eight Independent Resources. . . . . . . . . . . . . . . . . . . . . 11-3
11-2 Simultaneous Instruction Execution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-7
11-3 Derivation of Instruction Overlap Time. . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-8
11-4 Processor Activity – Even Alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-9
11-5 Processor Activity – Odd Alignment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-10
12-1 Signal Routing for Adapting the MC68030 to MC68020 Designs . . . . . . . 12-2
12-2 32-Bit Data Bus Coprocessor Connection . . . . . . . . . . . . . . . . . . . . . . . . . 12-6
12-3 Chip-Select Generation PAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-8
12-4 PAL Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-8
12-5 Bus Cycle Timing Diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-9
12-6 Example MC68030 Byte Select PAL System Configuration . . . . . . . . . . . 12-12
12-7 MC68030 Byte Select PAL Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-13
12-8 Access Time Computation Diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-15
12-9 Example Two-Clock Read, Three-Clock Write Memory Bank . . . . . . . . . . 12-19
12-10 Example PAL Equations for Two-Clock Memory Bank . . . . . . . . . . . . . . . 12-20
12-11 Additional Memory Enable Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-21
12-12 Example Two-Clock Read and Write Memory Bank . . . . . . . . . . . . . . . . . 12-22
12-13 Example PAL Equation for Two-Clock Read and Write Memory Bank . . . 12-23
12-14 Example 2-1-1-1 Burst Mode Memory Bank at 20 MHz, 256K Bytes . . . . 12-25
12-15 Example 3-1-1-1 Pipelined Burst Mode Memory Bank at
20 MHz, 256K Bytes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-28
12-16 Additional Memory Enable Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-29
12-17 Example MC68030 Hardware Configuration with
External Physical Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-33
12-18 Example Early Termination Control Circuit . . . . . . . . . . . . . . . . . . . . . . . . 12-34
12-19 Normal Instruction Boundaries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-37
12-20 Trace or Interrupt Exception. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-38
12-21 Other Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-38
12-22 Processor Halted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-39
12-23 Trace Interface Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-41
12-24 PAL Pin Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-44
12-25 Logic Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-45
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LIST OF TABLES
Table
Number Title Page
Number
1-1 Addressing Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11
1-2 Instruction Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-13
2-1 IS–I/IS Memory Indirection Encodings. . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-22
3-1 Data Movement Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5
3-2 Integer Arithmetic Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
3-3 Logical Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
3-4 Shift and Rotate Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8
3-5 Bit Manipulation Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9
3-6 Bit Field Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9
3-7 BCD Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10
3-8 Program Control Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-11
3-9 System Control Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12
3-10 MMU Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13
3-11 Multiprocessor Operations (Read-Modify-Write) . . . . . . . . . . . . . . . . . . . . 3-13
3-12 Condition Code Computations (Sheet 1 of 2) . . . . . . . . . . . . . . . . . . . . . . 3-15
3-13 Conditional Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17
3-14 Instruction Set Summary (Sheet 1 of 5). . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20
4-1 Address Space Encodings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5
5-1 Signal Index (Sheet 1 of 2). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2
5-2 Signal Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12
7-1 DSACK Codes and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7
7-2 Size Signal Encoding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9
7-3 Address OffsetEncodings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9
7-4 Data Bus Requirements for Read Cycles. . . . . . . . . . . . . . . . . . . . . . . . . . 7-10
7-5 MC68030 Internal to External Data Bus. . . . . . . . . . . . . . . . . . . . . . . . . . . 7-11
7-6 Memory Alignment and Port Size Influence on Write Bus Cycles . . . . . . . 7-19
7-7 Data Bus Write Enable Signals for Byte, Word, and Long-Word Ports . . . 7-23
7-8 DSACK, BERR, and HALT Assertion Results . . . . . . . . . . . . . . . . . . . . . . 7-79
7-9 STERM, BERR, and HALT Assertion Results . . . . . . . . . . . . . . . . . . . . . . 7-81
8-1 Exception Vector Assignments (Sheet 2 of 2) . . . . . . . . . . . . . . . . . . . . . . 8-2
8-2 Exception Vector Assignments (Sheet 1 of 2) . . . . . . . . . . . . . . . . . . . . . . 8-3
8-3 Microsequencer STATUS Indications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-4
8-4 Tracing Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-13
8-5 Interrupt Levels and Mask Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-16
8-6 Exception Priority Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-24
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Table
Number Title Page
Number
LIST OF TABLES (Continued)
9-1 Size Restrictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10
9-2 Translation Tree Selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-30
9-3 MMUSR Bit Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-60
10-1 cpTRAPcc Opmode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-19
10-2 Coprocessor Format Word Encodings. . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-22
10-3 Null Coprocessor Response Primitive Encodings . . . . . . . . . . . . . . . . . . . 10-39
10-4 Valid EffectiveAddress Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-43
10-5 Main Processor Control Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-51
10-6 Exceptions Related to Primitive Processing. . . . . . . . . . . . . . . . . . . . . . . . 10-66
12-1 Data Bus Activity for Byte, Word, and Long-Word Ports . . . . . . . . . . . . . . 12-11
12-2 Memory Access Time Equations at 20 MHz . . . . . . . . . . . . . . . . . . . . . . . 12-16
12-3 Calculated t
AVDV
Values for Operation at Frequencies
Less Than or Equal to the CPU Maximum Frequency Rating . . . . . . . . . 12-17
12-4 Microsequencer STATUS Indications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-36
12-5 List of Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-42
12-6 AS and ECSC Indicates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-43
12-7 V
CC
and GND Pin Assignments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-46
MOTOROLA
MC68030 USER’S MANUAL
1-1
SECTION 1
INTRODUCTION
The MC68030 is a second-generation full 32-bit enhanced microprocessor from Motorola.
The MC68030 is a member of the M68000 Family of devices that combines a central
processing unit (CPU) core, a data cache, an instruction cache, an enhanced bus controller,
and a memory management unit (MMU) in a single VLSI device. The processor is designed
to operate at clock speeds beyond 20 MHz. The MC68030 is implemented with 32-bit
registers and data paths, 32-bit addresses, a rich instruction set, and versatile addressing
modes.
The MC68030 is upward object code compatible with the earlier members of the M68000
Family and has the added features of an on-chip MMU, a data cache, and an improved bus
interface. It retains the flexible coprocessor interface pioneered in the MC68020 and
provides full IEEE floating-point support through this interface with the MC68881 or
MC68882 floating-point coprocessor. Also, the internal functional blocks of this
microprocessor are designed to operate in parallel, allowing instruction execution to be
overlapped. In addition to instruction execution, the internal caches, the on-chip MMU, and
the external bus controller all operate in parallel.
The MC68030 fully supports the nonmultiplexed bus structure of the MC68020, with 32 bits
of address and 32 bits of data. The MC68030 bus has an enhanced controller that supports
both asynchronous and synchronous bus cycles and burst data transfers. It also supports
the MC68020 dynamic bus sizing mechanism that automatically determines device port
sizes on a cycle-by-cycle basis as the processor transfers operands to or from external
devices.
A block diagram of the MC68030 is shown in Figure 1-1. The instructions and data required
by the processor are supplied from the internal caches whenever possible. The MMU
translates the logical address generated by the processor into a physical address utilizing
its address translation cache (ATC). The bus controller manages the transfer of data
between the CPU and memory or devices at the physical address.
Introduction
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MC68030 USER’S MANUAL
MOTOROLA
Figure 1-1. Block Diagram
MICROSEQUENCER AND
CONTROL
CONTROL
STORE
INSTRUCTION
CACHE
STAGE
B
STAGE
C
STAGE
D
INTERNAL
DATA
BUS
INSTRUCTION PIPE
INSTRUCTION
ADDRESS
BUS
ADDRESS
SECTION
PROGRAM
COUNTER
SECTION
DATA
SECTION
EXECUTION UNIT
MISALIGNMENT
MULTIPLEXER
SIZE
MULTIPLEXER DATA
PADS DATA
BUS
WRITE PENDING
BUFFER PREFETCH PENDING
BUFFER
MICROBUS
CONTROLLER
BUS CONTROLLER
BUS CONTROL
SIGNALS
ADDRESS
BUS
ADDRESS
PADS
ADDRESS
BUS
ADDRESS
DATA
CACHE
DATA
ADDRESS
BUS
CACHE
HOLDING
REGISTER
(CAHR)
ACCESS
CONTROL
UNIT
CONTROL
LOGIC
Introduction
MOTOROLA
MC68030 USER’S MANUAL
1-3
1.1 FEATURES
The features of the MC68030 microprocessor are:
• Object Code Compatible with the MC68020 and Earlier M68000 Microprocessors
• Complete 32-Bit Nonmultiplexed Address and Data Buses
• 16 32-Bit General-Purpose Data and Address Registers
• Two 32-Bit Supervisor Stack Pointers and 10 Special-Purpose Control Registers
• 256-Byte Instruction Cache and 256-Byte Data Cache Can Be Accessed Simulta-
neously
• Paged MMU that Translates Addresses in Parallel with Instruction Execution and Inter-
nal Cache Accesses
• Two Transparent Segments Allow Untranslated Access to Physical Memory To Be D
fined for Systems That Transfer Large Blocks of Data between Predefined Physical Ad-
dresses — e.g., Graphics Applications
• Pipelined Architecture with Increased Parallelism Allows Accesses to Internal Caches
To Occur in Parallel with Bus Transfers and Instruction Execution To Be Overlapped
• Enhanced Bus Controller Supports Asynchronous Bus Cycles (three clocks minimum),
Synchronous Bus Cycles (two clocks minimum), and Burst Data Transfers (one clock
minimum) all to the Physical Address Space
• Dynamic Bus Sizing Supports 8-, 16-, 32-Bit Memories and Peripherals
• Support for Coprocessors with the M68000 Coprocessor Interface — e.g., Full IEEE
Floating-Point Support Provided by the MC68881/MC68882 Floating-Point Coproces-
sors
• 4-Gbyte Logical and Physical Addressing Range
• Implemented in Motorola's HCMOS Technology That Allows CMOS and HMOS (High-
Density NMOS) Gates to be Combined for Maximum Speed, Low Power, and Optimum
Die Size
• Processor Speeds Beyond 20 MHz
Both improved performance and increased functionality result from the on-chip
implementation of the MMU and the data and instruction caches. The enhanced bus
controller and the internal parallelism also provide increased system performance. Finally,
the improved bus interface, the reduction in physical size, and the lower power consumption
combine to reduce system costs and satisfy cost/performance goals of the system designer.
Introduction
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MC68030 USER’S MANUAL
MOTOROLA
1.2 MC68030 EXTENSIONS TO THE M68000 FAMILY
In addition to the on-chip instruction cache present in the MC68020, the MC68030 has an
internal data cache. Data that is accessed during read cycles may be stored in the on-chip
cache, where it is available for subsequent accesses. The data cache reduces the number
of external bus cycles when the data operand required by an instruction is already in the
data cache.
Performance is enhanced further because the on-chip caches can be internally accessed in
a single clock cycle. In addition, the bus controller provides a two-clock cycle synchronous
mode and burst mode accesses that can transfer data in as little as one clock per long word.
The MC68030 enhanced microprocessor contains an on-chip MMU that allows address
translation to operate in parallel with the CPU core, the internal caches, and the bus
controller.
Additional signals support emulation and system analysis. External debug equipment can
disable the on-chip caches and the MMU to freeze the MC68030 internal state during
breakpoint processing. In addition, the MC68030 indicates:
1. The start of a refill of the instruction pipe
2. Instruction boundaries
3. Pending trace or interrupt processing
4. Exception processing
5. Halt conditions
This status and control information allows external debugging equipment to trace the
MC68030 activity and interact nonintrusively with the MC68030 to effectively reduce system
debug effort.
1.3 PROGRAMMING MODEL
The programming model of the MC68030 consists of two groups of registers: the user model
and the supervisor model. This corresponds to the user and supervisor privilege levels. User
programs executing at the user privilege level use the registers of the user model. System
software executing at the supervisor level uses the control registers of the supervisor level
to perform supervisor functions.
Introduction
MOTOROLA
MC68030 USER’S MANUAL
1-5
Figure 1-2 shows the user programming model, consisting of 16 32-bit general-purpose reg-
isters and two control registers:
• General-Purpose 32-Bit Registers (D0–D7, A0–A7)
• 32-Bit Program Counter (PC)
• 8-Bit Condition Code Register (CCR)
The supervisor programming model consists of the registers available to the user plus 14
control registers:
• Two 32-Bit Supervisor Stack Pointers (ISP and MSP)
• 16-Bit Status Register (SR)
• 32-Bit Vector Base Register (VBR)
• 32-Bit Alternate Function Code Registers (SFC and DFC)
• 32-Bit Cache Control Register (CACR)
• 32-Bit Cache Address Register (CAAR)
• 64-Bit CPU Root Pointer (CRP)
• 64-Bit Supervisor Root Pointer (SRP)
• 32-Bit Translation Control Register (TC)
• 32-Bit Transparent Translation Registers (TT0 and TT1)
• 16-Bit MMU Status Register (MMUSR)
The user programming model remains unchanged from previous M68000 Family
microprocessors. The supervisor programming model supplements the user programming
model and is used exclusively by the MC68030 system programmers who utilize the
supervisor privilege level to implement sensitive operating system functions, I/O control, and
memory management subsystems. The supervisor programming model contains all the
controls to access and enable the special features of the MC68030. This segregation was
carefully planned so that all application software is written to run at the nonprivileged user
level and migrates to the MC68030 from any M68000 platform without modification. Since
system software is usually modified by system programmers when ported to a new design,
the control features are properly placed in the supervisor programming model. For example,
the transparent translation feature of the MC68030 is new to the family supervisor
programming model for the MC68030 and the two translation registers are new additions to
the family supervisor programming model for the MC68030. Only supervisor code uses this
feature, and user application programs remain unaffected.
Introduction
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MC68030 USER’S MANUAL
MOTOROLA
Registers D0–D7 are used as data registers for bit and bit field (1 to 32 bits), byte (8 bit),
word (16 bit), long-word (32 bit), and quad-word (64 bit) operations. Registers A0–A6 and
the user, interrupt, and master stack pointers are address registers that may be used as
software stack pointers or base address registers. Register A7 (shown as A7' and A7'' in
Figure 1-3) is a register designation that applies to the user stack pointer in the user privilege
level and to either the interrupt or master stack pointer in the supervisor privilege level. In
the supervisor privilege level, the active stack pointer (interrupt or master) is called the
supervisor stack pointer (SSP). In addition, the address registers may be used for word and
long-word operations. All of the 16 general-purpose registers (D0–D7, A0–A7) may be used
as index registers.
Figure 1-2. User Programming Model
31 16 15 87
7
0
31 16 15 0
31 16 15
15
0
31 0
0CCR
PC
A7 (USP)
D0
D1
D2
D3
D4
D5
D6
D7
A0
A1
A2
A3
A4
A5
A6
DATA
REGISTERS
ADDRESS
REGISTERS
USER STACK
POINTER
PROGRAM
COUNTER
CONDITION
CODE
REGISTER
Introduction
MOTOROLA
MC68030 USER’S MANUAL
1-7
The program counter (PC) contains the address of the next instruction to be executed by the
MC68030. During instruction execution and exception processing, the processor
automatically increments the contents of the PC or places a new value in the PC, as
appropriate.
The status register, SR, (see Figure 1-4) stores the processor status. It contains the
condition codes that reflect the results of a previous operation and can be used for
conditional instruction execution in a program. The condition codes are extend (X), negative
(N), zero (Z), overflow (V), and carry (C). The user byte containing the condition codes is the
only portion of the status register information available in the user privilege level, and it is
referenced as the CCR in user programs. In the supervisor privilege level, software can
access the full status register, including the interrupt priority mask (three bits) as well as
additional control bits. These bits indicate whether the processor is in:
1. One of two trace modes (T1, T0)
2. Supervisor or user privilege level (S)
3. Master or interrupt mode (M)
The vector base register (VBR) contains the base address of the exception vector table in
memory. The displacement of an exception vector is added to the value in this register to
access the vector table.
Figure 1-3. Supervisor Programming Model Supplement
31 16 15 0
31 16 15 0
15 87 0
(CCR) SR
A7" (MSP)
A7' (ISP)
31 0VBR
SFC
DFC
CACR
CAAR
INTERRUPT
STACK POINTER
MASTER STACK
POINTER
STATUS REGISTER
VECTOR BASE
REGISTER
ALTERNATE FUNCTION
CODE REGISTERS
CACHE CONTROL
REGISTER
CACHE ADDRESS
REGISTER
0
0
0
31
31
31
AC0 ACCESS
CONTROL
REGISTER 0
0
31
AC1 ACCESS
CONTROL
REGISTER 1
0
31
ACUSR ACU STATUS
REGISTER
0
15
Introduction
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MC68030 USER’S MANUAL
MOTOROLA
Alternate function code registers, SFC and DFC, contain 3-bit function codes. Function
codes can be considered extensions of the 32-bit linear address that optionally provide as
many as eight 4-Gbyte address spaces. Function codes are automatically generated by the
processor to select address spaces for data and program at the user and supervisor
privilege levels and a CPU address space for processor functions (e.g., coprocessor
communications). Registers SFC and DFC are used by certain instructions to explicitly
specify the function codes for operations.
The cache control register (CACR) controls the on-chip instruction and data caches of the
MC68030. The cache address register (CAAR) stores an address for cache control
functions.
The CPU root pointer (CRP) contains a pointer to the root of the translation tree for the
currently executing task of the MC68030. This tree contains the mapping information for the
task's address space. When the MC68030 is configured to provide a separate address
space for supervisor routines, the supervisor root pointer (SRP) contains a pointer to the root
of the translation tree describing the supervisor's address space.
The translation control register (TC) consists of several fields that control address
translation. These fields enable and disable address translation, enable and disable the use
of SRP for the supervisor address space, and select or ignore the function codes in
translating addresses. Other fields define the size of memory pages, the number of address
bits used in translation, and the translation table structure.
The transparent translation registers, TT0 and TT1, can each specify separate blocks of
memory as directly accessible without address translation. Logical addresses in these areas
become the physical addresses for memory access. Function codes and the eight most
significant bits of the address can be used to define the area of memory and type of access;
either read, write, or both types of memory access can be directly mapped. The transparent
translation feature allows rapid movement of large blocks of data in memory or I/O space
without disturbing the context of the on-chip address translation cache or incurring delays
associated with translation table lookups. This feature is useful to graphics, controller, and
real-time applications.
Figure 1-4. Status Register
T1 T0 S M 0 I2 I1 I0 X N Z V C000
SYSTEM BYTE USER BYTE
(CONDITION CODE REGISTER)
TRACE
ENABLE INTERRUPT
PRIORITY MASK
SUPERVISOR/USER
STATE
MASTER/INTERRUPT
STATE EXTEND
NEGATIVE
ZERO
OVERFLOW
CARRY
15 14 13 12 11 10 9 8 7 56 43210
Introduction
MOTOROLA
MC68030 USER’S MANUAL
1-9
The MMU status register (MMUSR) contains memory management status information
resulting from a search of the address translation cache or the translation tree for a particular
logical address.
1.4 DATA TYPES AND ADDRESSING MODES
Seven basic data types are supported:
1. Bits
2. Bit Fields (Fields of consecutive bits, 1–32 bits long)
3. BCD Digits (Packed: 2 digits/byte, Unpacked: 1 digit/byte)
4. Byte Integers (8 bits)
5. Word Integers (16 bits)
6. Long-Word Integers (32 bits)
7. Quad-Word Integers (64 bits)
In addition, the instruction set supports operations on other data types such as memory
addresses. The coprocessor mechanism allows direct support of floating-point operations
with the MC68881 and MC68882 floating-point coprocessors as well as specialized user-
defined data types and functions.
The 18 addressing modes, shown in Table 1-1, include nine basic types:
1. Register Direct
2. Register Indirect
3. Register Indirect with Index
4. Memory Indirect
5. Program Counter Indirect with Displacement
6. Program Counter Indirect with Index
7. Program Counter Memory Indirect
8. Absolute
9. Immediate
The register indirect addressing modes can also postincrement, predecrement, offset, and
index addresses. The program counter relative mode also has index and offset capabilities.
As in the MC68020, both modes are extended to provide indirect reference through memory.
In addition to these addressing modes, many instructions implicitly specify the use of the
condition code register, stack pointer, and/or program counter.
1.5 INSTRUCTION SET OVERVIEW
The instructions in the MC68030 instruction set are listed in Table 1-2. The instruction set
has been tailored to support structured high-level languages and sophisticated operating
systems. Many instructions operate on bytes, words, or long words, and most instructions
can use any of the 18 addressing modes.
Introduction
1-10
MC68030 USER’S MANUAL
MOTOROLA
NOTES:
Dn = Data Register, D0–D7
An = Address Register, A0–A7
8,
d
16 = A twos-complement or sign-extended displacement; added as part of the effective address
calculation; size is 8 (d
8
) or 16 (d
16
) bits; when omitted, assemblers use a value of zero.
Xn = Address or data register used as an inde x register; form is Xn.SIZE*SCALE, where SIZE is .W
or .L indicates index register size) and SCALE is 1, 2, 4, or 8 (index register is multiplied by
SCALE); use of SIZE and/or SCALE is optional.
bd = A twos-complement base displacement;when present, size can be 16 or 32 bits.
od = Outer displacement, added as part of effective address calculation after any memory
indirection; use is optional with asize of 16 or 32 bits.
PC = Program Counter
(data) = Immediate value of 8, 16, or 32 bits
( ) = Effective Address
[ ] = Use as indirect access to long-word address.
Table 1-1. Addressing Modes
Addressing Modes Syntax
Register Direct
Data Register Direct
Address Register Direct Dn
An
Register Indirect
Address Register Indirect
Address Register Indirect with Postincrement
Address Register Indirect with Predecrement
Address Register Indirect with Displacement
(An)
(An)
–(An)
(d
16
,An)
Register Indirect with Index
Address Register Indirect with Index (8-BitDisplacement)
Address Register Indirect with Index (Base Displacement) (d
8
,An,Xn)
(bd,An,Xn)
Memory Indirect
Memory Indirect Postindexed
Memory Indirect Preindexed ([bd,An],Xn,od)
([bd,An,Xn],od)
Program Counter Indirect with Displacement (d
16
,PC)
Program Cou nter Indirect with IndexPC Indirect with Index (8-Bit
Displacement)
PC Indirect with Index (Base Displacement)
(d
8
,PC,Xn)
(bd,PC,Xn)
Program Counter Memory Indirect
PC Memory Indirect Postindexed
PC Memory Indirect Preindexed ([bd,PC],Xn,od)
([bd,PC,Xn],od)
Absolute
Absolute Short
Absolute Long (xxx).W
(xxx).L
Immediate #(data)
Introduction
MOTOROLA
MC68030 USER’S MANUAL
1-11
1.6 VIRTUAL MEMORY AND VIRTUAL MACHINE CONCEPTS
The full addressing range of the MC68030 is 4 Gbytes (4,294,967,296 bytes) in each of eight
address spaces. Even though most systems implement a smaller physical memory, the
system can be made to appear to have a full 4 Gbytes of memory available to each user
program by using virtual memory techniques.
In a virtual memory system, a user program can be written as if it has a large amount of
memory available, when the physical memory actually present is much smaller. Similarly, a
system can be designed to allow user programs to access devices that are not physically
present in the system, such as tape drives, disk drives, printers, terminals, and so forth. With
proper software emulation, a physical system can appear to be any other M68000 computer
system to a user program, and the program can be given full access to all of the resources
of that emulated system. Such an emulated system is called a virtual machine.
1.6.1 Virtual Memory
A system that supports virtual memory has a limited amount of high-speed physical memory
that can be accessed directly by the processor and maintains an image of a much larger
virtual memory on a secondary storage device such as a large-capacity disk drive. When
the processor attempts to access a location in the virtual memory map that is not resident in
physical memory, a page fault occurs. The access to that location is temporarily suspended
while the necessary data is fetched from secondary storage and placed in physical memory.
The suspended access is then either restarted or continued.
The MC68030 uses instruction continuation to support virtual memory. When a bus cycle is
terminated with a bus error, the microprocessor suspends the current instruction and
executes the virtual memory bus error handler. When the bus error handler has completed
execution, it returns control to the program that was executing when the error was detected,
reruns the faulted bus cycle (when required), and continues the suspended instruction.
Introduction
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MC68030 USER’S MANUAL
MOTOROLA
Table 1-2. Instruction Set
Mnemonic Description Mnemonic Description
ABCD Add Decimal with Extend MOVE USP Move User Stack Pointer
ADD Add MOVEC Move Control Register
ADDA Add Address MOVEM Move Multiple Registers
ADDI Add Immediate MOVEP Move Periphral
ADDQ Add Quick MOVEQ Move Quick
ADDX Add with Extend MOVES Move Alternate Address Space
AND Logical AND MULS Signed Multiply
ANDI Logical AND Immediate MULU Unsigned Multiply
ASL, ASR Arithmatic Shift Left and Right NBCD Negate Decimal with Extend
Bcc Branch Conditionally NEG Negate
BCHG Test Bit and Change NEGX Negate with Extend
BCLR Test Bit and Clear NOP No Operation
BFCHG Test Bit Feild and Change NOT Logical Compliment
BFCLR Test Bit Feild and Clear OR Logical Inclusive OR
BFEXTS Signed Bit Feild Extract ORI Logical Inclusive OR Immediate
BFEXTU Unsigned Bit Feild Extract ORI CCR Logical Inclusive OR Immediate to
BFFO Bit Feild Find First One Condition Codes
BFINS Bit Feild Insert ORI SR Logical Inclusive OR Immediate to
BFSET Test Bit Feild and Set Status Register
BFTST Test Bit Feild PACK Pack BCD
BKPT Breakpoint PEA Push Effective Address
BRA Branch PFLUSH Flush Entry(ies) in the ATC
BSET Test Bit and Set PFLUSHA Flush All Entries in the ATC
BSR Branch to Subroutine PLOADR, Load Entry into the ATC
BTST Test Bit PLOADW
CAS Compare and Swap Operands PMOVE Move to-from MMU Registers
CAS 2 Compare and Swap Dual Operands PMOVEFD Move to-from MMU Registers with
CHK Check Register Against Bound Flush Disable
CHK2 Check Register Against Upper and PTESTR Test a Logical Address
Lower Bounds PTESTW
CLR Clear RESET Reset External Devices
CMP Compare ROL, ROR Rotate Left and Right
CMPA Compare Address ROXL, ROXR Rotate With Extend Left and Right
CMPI Compare Immediate RTD Return and Deallocate
CMPM Compare Memory to Memory RTE Return from Exception
CMP2 Compare Registre Against Upper and RTR Return and Restore Codes
Lower Bounds RTS Return from Subroutine
DBcc Test Condition, Decrement and Branch SBCD Subtract Decimal With Extend
DIVS, DIVSL Signed Divide Scc Set Conditionally
DIVU, DIVUL Unsigned Divide STOP Stop
EOR Logical Exclusive OR SUB Subtract
EORI Logical Exclusive OR Immediate SUBA Subtract Immediate
EXG Exchange Registers SUBI Subtract Quick
EXT, EXTB Sign Extend SUBQ Subtract with Extend
ILLEGAL Take Illegal Instruction Trap SUBX Swap Register Words
JMP Jump SWAP Test Operand and Set
JSR Jump to Subroutine TAS Trap
LEA Load Effective Address TRAP Trap Conditionally
LINK Link and Allocate TRAPcc Trap on Overflow
LSL, LSR Logical Shift Left and Right TRAPV Test on Overflow
MOVE Move TST Test Operand
MOVEA Move Address UNLK
UNPK Unlink
Unpack BCD
MOVE CCR Move Condition Code Register
MOVE SR Move Status Register
Introduction
MOTOROLA
MC68030 USER’S MANUAL
1-13
1.6.2 Virtual Machine
A typical use for a virtual machine system is the development of software, such as an
operating system, for a new machine also under development and not yet available for
programming use. In a virtual machine system, a governing operating system emulates the
hardware of the new machine and allows the new software to be executed and debugged
as though it were running on the new hardware. Since the new software is controlled by the
governing operating system, it is executed at a lower privilege level than the governing
operating system. Thus, any attempts by the new software to use virtual resources that are
not physically present (and should be emulated) are trapped to the governing operating
system and performed by its software.
In the MC68030 implementation of a virtual machine, the virtual application runs at the user
privilege level. The governing operating system executes at the supervisor privilege level
and any attempt by the new operating system to access supervisor resources or execute
privileged instructions causes a trap to the governing operating system.
Instruction continuation is used to support virtual I/O devices in memory-mapped input/
output systems. Control and data registers for the virtual device are simulated in the memory
map. An access to a virtual register causes a fault and the function of the register is
emulated by software.
Mnemonic Description Mnemonic Description
cpBcc
cpDBcc
cpGEN
Branch Conditionally
Test Coprocessor Condition,
Decrement and Branch
Coprocessor General Instruction
cpRESTORE
cpSAVE
cpScc
cpTRAPcc
Restore Internal State of Coprocessor
Save Internal State of Coprocessor
Set Conditionally
Trap Conditionally
Introduction
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MC68030 USER’S MANUAL
MOTOROLA
1.7 THE MEMORY MANAGEMENT UNIT
The MMU supports virtual memory systems by translating logical addresses to physical ad-
dresses using translation tables stored in memory. The MMU stores address mappings in
an address translation cache (ATC) that contains the most recently used translations. When
the ATC contains the address for a bus cycle requested by the CPU, a translation table
search is not performed. Features of the MMU include:
• Multiple Level Translation Tables with Short- and Long-Format Descriptors for Efficient
Table Space Usage
• Table Searches Automatically Performed in Microcode
• 22-Entry Fully Associative ATC
• Address Translations and Internal Instruction and Data Cache Accesses Performed in
Parallel
• Eight Page Sizes Available Ranging from 256 to 32K Bytes
• Two Optional Transparent Blocks
• User and Supervisor Root Pointer Registers
• Write Protection and Supervisor Protection Attributes
• Translations Enabled/Disabled by Software
• Translations Can Be Disabled with External MMUDIS Signal
• Used and Modified Bits Automatically Maintained in Tables and ATC
• Cache Inhibit Output (CIOUT) Signal Can Be Asserted on a Page-by-Page Basis
• 32-Bit Internal Logical Address with Capability To Ignore as many as 15 Upper Address
Bits
• 3-Bit Function Code Supports Separate Address Spaces
• 32-Bit Physical Address
The memory management function performed by the MMU is called demand paged memory
management. Since a task specifies the areas of memory it requires as it executes, memory
allocation is supported on a demand basis. If a requested access to memory is not currently
mapped by the system, then the access causes a demand for the operating system to load
or allocate the required memory image. The technique used by the MC68030 is paged
memory management because physical memory is managed in blocks of a specified
number of bytes, called page frames. The logical address space is divided into fixed-size
pages that contain the same number of bytes as the page frames. Memory management
assigns a physical base address to a logical page. The system software then transfers data
between secondary storage and memory one or more pages at a time.
Introduction
MOTOROLA
MC68030 USER’S MANUAL
1-15
1.8 PIPELINED ARCHITECTURE
The MC68030 uses a three-stage pipelined internal architecture to provide for optimum
instruction throughput. The pipeline allows as many as three words of a single instruction or
three consecutive instructions to be decoded concurrently.
1.9 THE CACHE MEMORIES
Due to locality of reference, instructions and data that are used in a program have a high
probability of being reused within a short time. Additionally, instructions and data operands
that reside in proximity to the instructions and data currently in use also have a high
probability of being utilized within a short period. To exploit these locality characteristics, the
MC68030 contains two on-chip logical caches, a data cache, and an instruction cache.
Each of the caches stores 256 bytes of information, organized as 16 entries, each containing
a block of four long words (16 bytes). The processor fills the cache entries either one long
word at a time or, during burst mode accesses, four long words consecutively. The burst
mode of operation not only fills the cache efficiently but also captures adjacent instruction or
data items that are likely to be required in the near future due to locality characteristics of
the executing task.
The caches improve the overall performance of the system by reducing the number of bus
cycles required by the processor to fetch information from memory and by increasing the
bus bandwidth available for other bus masters in the system. Addition of the data cache in
the MC68030 extends the benefits of cache techniques to all memory accesses. During a
write cycle, the data cache circuitry writes data to a cached data item as well as to the item
in memory, maintaining consistency between data in the cache and that in memory.
However, writing data that is not in the cache may or may not cause the data item to be
stored in the cache, depending on the write allocation policy selected in the cache control
register (CACR).
MOTOROLA
MC68030 USER’S MANUAL
2-1
SECTION 2
DATA ORGANIZATION AND ADDRESSING
CAPABILITIES
Most external references to memory by a microprocessor are either program references or
data references; they either access instruction words or operands (data items) for an
instruction. Program references are references to the program space, the section of memory
that contains the program instructions and any immediate data operands that reside in the
instruction stream. Refer to M68000PM/AD,
M68000 Programmer's Reference Manual
, for
descriptions of the instructions in the program space. Data references refer to the data
space, the section of memory that contains the program data. Data items in the instruction
stream can be accessed with the program counter relative addressing modes, and these
accesses are classified as program references. A third type of external reference used for
coprocessor communications, interrupt acknowledge cycles, and breakpoint acknowledge
cycles is classified as a CPU space reference. The MC68030 automatically sets the function
codes to access the program space, the data space, or the CPU space for special functions
as required. The function codes can be used by the memory management unit to organize
separate program (read only) and data (read-write) memory areas.
This section describes the data organization and addressing capabilities of the MC68030. It
lists the types of operands used by instructions and describes the registers and their use as
operands. Next, the section describes the organization of data in memory and the
addressing modes available to access data in memory. Last, the section describes the
system stack and user program stacks and queues.
2.1 INSTRUCTION OPERANDS
The MC68030 supports a general-purpose set of operands to serve the requirements of a
large range of applications. Operands of MC68030 instructions may reside in registers, in
memory, or within the instructions themselves. An instruction operand might also reside in
a coprocessor. An operand may be a single bit, a bit field of from 1 to 32 bits in length, a byte
(8 bits), a word (16 bits), a long word (32 bits), or a quad word (64 bits). The operand size
for each instruction is either explicitly encoded in the instruction or implicitly defined by the
instruction operation. Coprocessors are designed to support special computation models
that require very specific but widely varying data operand types and sizes. Hence,
coprocessor instructions can specify operands of any size.
Data Organization and Addressing Capabilities
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2.2 ORGANIZATION OF DATA IN REGISTERS
The eight data registers can store data operands of 1, 8, 16, 32, and 64 bits, addresses of
16 or 32 bits, or bit fields of 1 to 32 bits. The seven address registers and the three stack
pointers are used for address operands of 16 or 32 bits. The control registers (SR, VBR,
SFC, DFC, CACR, CAAR, CRP, SRP, TC, TT0, TT1, and MMUSR) vary in size according
to function. Coprocessors may define unique operand sizes and support them with on-chip
registers accordingly.
2.2.1 Data Registers
Each data register is 32 bits wide. Byte operands occupy the low-order 8 bits, word
operands the low-order 16 bits, and long-word operands the entire 32 bits. When a data
register is used as either a source or destination operand, only the appropriate low-order
byte or word (in byte or word operations, respectively) is used or changed; the remaining
high-order portion is neither used nor changed. The least significant bit of a long-word
integer is addressed as bit zero, and the most significant bit is addressed as bit 31. For bit
fields, the most significant bit is addressed as bit zero, and the least significant bit is
addressed as the width of the field minus one. If the width of the field plus the offset is greater
than 32, the bit field wraps around within the register. The following illustration shows the
organization of various types of data in the data registers.
Quad-word data consists of two long words; for example, the product of 32-bit multiply or
the quotient of 32-bit divide operations (signed and unsigned). Quad words may be
organized in any two data registers without restrictions on order or pairing. There are no
explicit instructions for the managment of this data type, although the MOVEM instruction
can be used to move a quad word into or out of the registers.
Binary-coded decimal (BCD) data represents decimal numbers in binary form. Although
many BCD codes have been devised, the BCD instructions of the M68000 Family support
formats which the four least significant bits consist of a binary number having the numeric
value of the corresponding decimal number. Two BCD formats are used. In the unpacked
BCD format, a byte contains one digit; the four least significant bits contain the binary value
and the four most significant bits are undefined. Each byte of the packed BCD format
contains two digits; the least significant four bits contain the least significant digit.
Data Organization and Addressing Capabilities
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MC68030 USER’S MANUAL
2-3
Note: If width + offset < 32, bit filed wraps around within the register.
Data Organization in Data Registers
Bit
≤
(0 Modulo (Offset)<31, Offset of 0 = MSB)
31 30 29 10
MSB
•••
LSB
Byte
31 24 23 16 15 8 7 0
High-Order Byte Middle-High Byte Middle-Low Byte Low-Order Byte
16-Bit Word
31 16 15 0
High-Order Word Low-Order W ord
Long Word
31 0
Long Word
Quad Word
63 62 32
MSB Any Dx
31 0
Offset MSB
•••
LSB
Bit Field (0
≤
Offset<32, 0<Width
≤
32)
31 0
Long Word
Unpacked BCD (a = MSB)
31 876543210
xxxxabcd
Packed BCD (a = MSB First Digit, e = MSB Second Digit)
31 876543210
abcdefgh
Data Organization and Addressing Capabilities
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MOTOROLA
2.2.2 Address Registers
Each address register and stack pointer is 32 bits wide and holds a 32-bit address. Address
registers cannot be used for byte-sized operands. Therefore, when an address register is
used as a source operand, either the low-order word or the entire long-word operand is
used, depending upon the operation size. When an address register is used as the
destination operand, the entire register is affected, regardless of the operation size. If the
source operand is a word size, it is first sign-extended to 32 bits and then used in the
operation to an address register destination. Address registers are used primarily for
addresses and to support address computation. The instruction set includes instructions
that add to, subtract from, compare, and move the contents of address registers. The
following example shows the organization of addresses in address registers.
Address Organization in Address Registers
2.2.3 Control Registers
The control registers described in this section contain control information for supervisor
functions and vary in size. With the exception of the user portion of the status register (CCR),
they are accessed only by instructions at the supervisor privilege level.
The status register (SR), shown in Figure 1–4, is 16 bits wide. Only 12 bits of the status
register are defined; all undefined values are reserved by Motorola for future definition. The
undefined bits are read as zeros and should be written as zeros for future compatibility. The
lower byte of the status register is the CCR. Operations to the CCR can be performed at the
supervisor or user privilege level. All operations to the status register and CCR are word-
sized operations, but for all CCR operations, the upper byte is read as all zeros and is
ignored when written, regardless of privilege level.
31 16 15 0
Sign-Extended 16-Bit Address Operand
31 0
Full 32-Bit Address Operand
Data Organization and Addressing Capabilities
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2-5
The supervisor programming model (see Figure 1–3) shows the control registers. The cache
control register (CACR) provides control and status information for the on-chip instruction
and data caches. The cache address register (CAAR) contains the address for cache control
functions. The vector base register (VBR) provides the base address of the exception vector
table. All operations involving the CACR, CAAR, and VBR are long-word operations,
whether these registers are used as the source or the destination operand.
The alternate function code registers (SFC and DFC)
are 32-bit registers with only bits 2:0 implemented that contain the address space values
(FC0-FC2) for the read or write operands of MOVES, PLOAD, PFLUSH, and PTEST
instructions. The MOVEC instruction is used to transfer values to and from the alternate
function code registers. These are long-word transfers; the upper 29 bits are read as zeros
and are ignored when written.
The remaining control registers in the supervisor programming model are used by the
memory management unit (MMU). The CPU root pointer (CRP) and supervisor root pointer
(SRP) contain pointers to the user and supervisor address translation trees. Transfers of
data to and from these 64-bit registers are quad-word transfers. The translation control
register (TC) contains control information for the MMU. The MC68030 always uses long-
word transfers to access this 32-bit register. The transparent translation registers (TT0 and
TT1) also contain 32 bits each; they identify memory areas for direct addressing without
address translation. Data transfers to and from these registers are long-word transfers. The
MMU status register (MMUSR) stores the status of the MMU after execution of a PTEST
instruction. It is a 16-bit register, and transfers to and from the MMUSR are word transfers.
Refer to
Section 9 Memory Management Unit
for more detail.
2.3 ORGANIZATION OF DATA IN MEMORY
Memory is organized on a byte-addressable basis where lower addresses correspond to
higher order bytes. The address, N, of a long-word data item corresponds to the address of
the most significant byte of the highest order word. The lower order word is located at
address N + 2, leaving the least significant byte at address N + 3 (refer to Figure 2–1). Notice
that the MC68030 does not require data to be aligned on word boundaries (refer to Figure
2–2), but the most efficient data transfers occur when data is aligned on the same byte
boundary as its operand size. However, instruction words must be aligned on word
boundaries.
Data Organization and Addressing Capabilities
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MOTOROLA
The data types supported in memory by the MC68030 are bit and bit field data; integer data
of 8, 16, or 32 bits; 32-bit addresses; and BCD data (packed and unpacked). These data
types are organized in memory as shown in Figure 2–2. Note that all of these data types can
be accessed at any byte address.
Coprocessors can implement any data types and lengths up to 255 bytes. For example, the
MC68881/MC68882 floating-point coprocessors support memory accesses for quad-word-
sized items (double-precision floating-point values).
Figure 2A bit operand is specified by a base address that selects one byte in memory (the
base byte) and a bit number that selects the one bit in this byte. The most significant bit of
the byte is bit 7.
Figure 2-1. Memory Operand Address
31 23 15 7 0
BYTE $00000000
WORD $00000000
LONG WORD $00000000
BYTE $00000001 BYTE $00000002 BYTE $00000003
WORD $00000002
BYTE $00000004
WORD $00000004
LONG WORD $00000004
BYTE $00000005 BYTE $00000006 BYTE $00000007
WORD $00000006
BYTE $FFFFFFFC
WORD $FFFFFFFC
LONG WORD $FFFFFFFC
BYTE $FFFFFFFD BYTE $FFFFFFFE BYTE $FFFFFFFF
WORD $FFFFFFFE
Data Organization and Addressing Capabilities
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MC68030 USER’S MANUAL
2-7
Figure 2-2. Memory Data Organization
07707070
07707070
07707070
077 07070
07707070
07 07 07 0
BYTE n - 1 BYTE n + 1
7 6 5 4 3 2 1 0 BYTE n + 2
BASE ADDRESS BIT NUMBER
BIT DATA
BYTE n - 1
BIT FIELD DATA BASE BIT
BYTE n 0 1 2 3 ...........w - 1
WIDTHOFFSET
OFFSET
...3-2-1 0 1 2...
BASE ADDRESS
BYTE n - 1 BYTE n + 2
BYTE INTEGER DATA
BYTE n + 1MSB BYTE n LSB
ADDRESS
WORD INTEGER BYTE n + 2 BYTE n + 3
ADDRESS
WORD INTEGER DATA
7
0
77 0
7
007 07 0
70
77 0 LONG-WORD INTEGER BYTE n + 4
70 07 07 0
70
77 0
ADDRESS
BYTE n - 1
QUAD WORD BYTE n + 8
BYTE n - 1
QUAD-WORD DATA
BYTE n - 1 BYTE n + 2BYTE n + 1MSD LSD
ADDRESS
PACKED BINARY-CODED DATA
43
BYTE n - 1 BYTE n + 2
XX MSD
ADDRESS
43 XX LSD
43
XX = USER DEFINED VALUE
ADDRESS
UNPACKED BINARY-CODED DATA
BYTE n - 1
Data Organization and Addressing Capabilities
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MOTOROLA
A bit field operand is specified by:
1. A base address that selects one byte in memory,
2. A bit field offset that indicates the leftmost (base) bit of the bit field in relation to the
most significant bit of the base byte, and
3. A bit field width that determines how many bits to the right of the base bit are in the bit
field.
The most significant bit of the base byte is bit field offset 0, the least significant bit of the
base byte is bit field offset 7, and the least significant bit of the previous byte in memory is
bit offset –1. Bit field offsets may have values in the range of –2
31
to 2
31
–1, and bit field
widths may range between 1 and 32 bits.
2.4 ADDRESSING MODES
The addressing mode of an instruction can specify the value of an operand (with an
immediate operand), a register that contains the operand (with the register direct addressing
mode), or how the effective address of an operand in memory is derived. An assembler
syntax has been defined for each addressing mode.
Figure 2–3 shows the general format of the single effective address instruction operation
word. The effective address field specifies the addressing mode for an operand that can use
one of the numerous defined modes. The (eaL designation is composed of two 3-bit fields:
the mode field and the register field. The value in the mode field selects one or a set of
addressing modes. The register field specifies a register for the mode or a submode for
modes that do not use registers.
Figure 2-3. Single Effective Address
Many instructions imply the addressing mode for one of the operands. The formats of these
instructions include appropriate fields for operands that use only one addressing mode.
15 14 13 12 11 10 9 8 7 6 5 0
X XXXXXXXXX EFFECTIVE ADDRESS
MODE REGISTER
Data Organization and Addressing Capabilities
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MC68030 USER’S MANUAL
2-9
The effective address field may require additional information to fully specify the operand
address. This additional information, called the effective address extension, is contained in
an additional word or words and is considered part of the instruction. Refer to
2.5 Effective
Address Encoding Summary
for a description of the extension word formats.
The notational conventions used in the addressing mode descriptions in this section are:
EA — Effective address
An — Address register n
Example: A3 is address register 3
Dn — Data register n
Example: D5 is data register 5
Xn.SIZE*SCALE — Denotes index register n (data or address), the index size
(W for word, L for long word), and a scale factor (1, 2, 4,
or 8 for no, word, long-word, or quad-word scaling, respectively).
PC — The program counter
d
n
— Displacement value, n bits wide
bd — Base displacement
od — Outer displacement
L — Long-word size
W — Word size
( ) — Identify an indirect address in a register
[ ] — Identify an indirect address in memory
When the addressing mode uses a register, the register field of the operation word specifies
the register to be used. Other fields within the instruction specify whether the register
selected is an address or data register and how the register is to be used.
2.4.1 Data Register Direct Mode
In the data register direct mode, the operand is in the data register specified by the effective
address register field.
OPERAND
GENERATION:
ASSEMBLER SYNTAX:
MODE:
REGISTER:
DATA REGISTER:
NUMBER OF EXTENSION WORDS:
EA = Dn
Dn
000
n
Dn
0
31 0
OPERAND
Data Organization and Addressing Capabilities
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MOTOROLA
2.4.2 Address Register Direct Mode
In the address register direct mode, the operand is in the address register specified by the
effective address register field.
2.4.3 Address Register Indirect Mode
In the address register indirect mode, the operand is in memory, and the address of the
operand is in the address register specified by the register field.
2.4.4 Address Register Indirect with Postincrement Mode
In the address register indirect with postincrement mode, the operand is in memory, and the
address of the operand is in the address register specified by the register field. After the
operand address is used, it is incremented by one, two, or four depending on the size of the
operand: byte, word, or long word. Coprocessors may support incrementing for any size of
operand up to 255 bytes. If the address register is the stack pointer and the operand size is
byte, the address is incremented by two rather than one to keep the stack pointer aligned to
a word boundary.
31 0
OPERAND
EA = An
An
001
n
An
0
GENERATION:
ASSEMBLER SYNTAX:
MODE:
REGISTER:
ADDRESS REGISTER:
NUMBER OF EXTENSION WORDS:
31 0
31 0
GENERATION:
ASSEMBLER SYNTAX:
MODE:
REGISTER:
ADDRESS REGISTER:
MEMORY ADDRESS:
NUMBER OF EXTENSION WORDS:
EA = (An)
(An)
010
n
An
OPERAND
MEMORY ADDRESS
0
31 0
31 0
+
MEMORY ADDRESS
OPERAND
MEMORY ADDRESS:
NUMBER OF EXTENSION WORDS:
OPERAND LENGTH ( 1, 2, OR 4):
GENERATION:
ASSEMBLER SYNTAX:
MODE:
REGISTER:
ADDRESS REGISTER:
0
EA = (An)
An = An + SIZE
(An) +
011
n
An
Data Organization and Addressing Capabilities
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MC68030 USER’S MANUAL
2-11
2.4.5 Address Register Indirect with Predecrement Mode
In the address register indirect with predecrement mode, the operand is in memory, and the
address of the operand is in the address register specified by the register field. Before the
operand address is used, it is decremented by one, two, or four depending on the operand
size: byte, word, or long word. Coprocessors may support decrementing for any operand
size up to 255 bytes. If the address register is the stack pointer and the operand size is byte,
the address is decremented by two rather than one to keep the stack pointer aligned to a
word boundary.
31 0
31 0
MEMORY ADDRESS
OPERAND
MEMORY ADDRESS:
NUMBER OF EXTENSION WORDS: 0
OPERAND LENGTH (1, 2, OR 4):
An = An – SIZE
EA = (An)
– (An)
100
n
An
GENERATION:
ASSEMBLER SYNTAX:
MODE:
REGISTER:
ADDRESS REGISTER:
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2.4.6 Address Register Indirect with Displacement Mode
In the address register indirect with displacement mode, the operand is in memory. The
address of the operand is the sum of the address in the address register plus the sign-
extended 16-bit displacement integer in the extension word. Displacements are always sign-
extended to 32 bits prior to being used in effective address calculations.
2.4.7 Address Register Indirect with Index (8-Bit Displacement) Mode
This addressing mode requires one extension word that contains the index register indicator
and an 8-bit displacement. The index register indicator includes size and scale information.
In this mode, the operand is in memory. The address of the operand is the sum of the
contents of the address register, the sign-extended displacement value in the low-order
eight bits of the extension word, and the sign-extended contents of the index register
(possibly scaled). The user must specify the displacement, the address register, and the
index register in this mode.
31 0
31 0
EA = (An) + d
(d ,An)
101
n
An
GENERATION:
ASSEMBLER SYNTAX:
MODE:
REGISTER:
ADDRESS REGISTER:
MEMORY ADDRESS:
NUMBER OF EXTENSION WORDS: 1 OPERAND
+
SIGN EXTENDED INTEGER 031 15
16
16
MEMORY ADDRESS
DISPLACEMENT:
31 0
31 0
31 0
MEMORY ADDRESS
OPERAND
MEMORY ADDRESS:
NUMBER OF EXTENSION WORDS:
EA = (An) + (XN) + d
(d ,An,Xn.SIZE*SCALE)
110
n
An
GENERATION:
ASSEMBLER SYNTAX:
MODE:
REGISTER:
ADDRESS REGISTER:
INTEGER
SIGN-EXTENDED VALUE
SCALE VALUE
+
0
0
+
X
31
DISPLACEMENT:
INDEX REGISTER
SCALE:
1
70
7
SIGN EXTENDED
8
8
31
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2.4.8 Address Register Indirect with Index (Base Displacement) Mode
This addressing mode requires an index register indicator and an optional 16- or 32-bit sign-
extended base displacement. The index register indicator includes size and scaling
information. The operand is in memory. The address of the operand is the sum of the
contents of the address register, the scaled contents of the sign-extended index register,
and the base displacement.
In this mode, the address register, the index register, and the displacement are all optional.
If none is specified, the effective address is zero. This mode provides a data register indirect
address when no address register is specified and the index register is a data register (Dn).
31 0
31 0
31 0
31 0
MEMORY ADDRESS:
NUMBER OF EXTENSION WORDS: 1,2, OR 3
EA = (An) + (Xn) + bd
(bd,An,Xn.SIZE*SCALE)
110
n
An
GENERATION:
ASSEMBLER SYNTAX:
MODE:
REGISTER:
ADDRESS REGISTER:
SIGN-EXTENDED VALUE
SIGN-EXTENDED VALUE
SCALE VALUE
OPERAND
+
+
X
BASE DISPLACEMENT:
INDEX REGISTER:
SCALE:
MEMORY ADDRESS
70
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2.4.9 Memory Indirect Postindexed Mode
In this mode, the operand and its address are in memory. The processor calculates an
intermediate indirect memory address using the base register (An) and base displacement
(bd). The processor accesses a long word at this address and adds the index operand
(Xn.SIZE*SCALE) and the outer displacement to yield the effective address. Both
displacements and the index register contents are sign-extended to 32 bits.
In the syntax for this mode, brackets enclose the values used to calculate the intermediate
memory address. All four user-specified values are optional. Both the base and outer
displacements may be null, word, or long word. When a displacement is omitted or an
element is suppressed, its value is taken as zero in the effective address calculation.
31 0
31 0
31 0
31 0
31 0
31 0
EFFECTIVE ADDRESS:
NUMBER OF EXTENSION WORDS: 1,2, 3, 4, OR 5
EA = (bd + An) + Xn.SIZE*SCALE + od
([bd,An],Xn.SIZE*SCALE,od)
110
An
GENERATION:
ASSEMBLER SYNTAX:
MODE:
ADDRESS REGISTER:
SIGN-EXTENDED VALUE
SCALE VALUE
OPERAND
+
+
31 0
BASE DISPLACEMENT:
INDEX REGISTER:
SCALE:
MEMORY ADDRESS
INDIRECT MEMORY ADDRESS
VALUE AT INDIRECT MEMORY ADDRESS
POINTS TO
SIGN-EXTENDED VALUE
SIGN-EXTENDED VALUE
+
X
OUTER DISPLACEMENT:
0
7
Data Organization and Addressing Capabilities
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2.4.10 Memory Indirect Preindexed Mode
In this mode, the operand and its address are in memory. The processor calculates an
intermediate indirect memory address using the base register (An), a base displacement
(bd), and the index operand (Xn.SIZE * SCALE). The processor accesses a long word at
this address and adds the outer displacement to yield the effective address. Both
displacements and the index register contents are sign-extended to 32 bits.
In the syntax for this mode, brackets enclose the values used to calculate the intermediate
memory address. All four user-specified values are optional. Both the base and outer
displacements may be null, word, or long word. When a displacement is omitted or an
element is suppressed, its value is taken as zero in the effective address calculation.
31 0
SIGN-EXTENDED VALUE
31 0
31 0
31 0
31 0
31 0
31 0
EFFECTIVE ADDRESS:
NUMBER OF EXTENSION WORDS: 1,2, 3, 4, OR 5
EA = (bd + An + Xn.SIZE*SCALE) + od
([bd,An,Xn.SIZE*SCALE],od)
110
An
GENERATION:
ASSEMBLER SYNTAX:
MODE:
ADDRESS REGISTER:
SCALE VALUE
OPERAND
+
7
+
BASE DISPLACEMENT:
INDEX REGISTER:
SCALE:
MEMORY ADDRESS
INDIRECT MEMORY ADDRESS
VALUE AT INDIRECT MEMORY ADDRESS
POINTS TO
SIGN-EXTENDED VALUE
SIGN-EXTENDED VALUE
+
X
OUTER DISPLACEMENT:
0
Data Organization and Addressing Capabilities
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2.4.11 Program Counter Indirect with Displacement Mode
In this mode, the operand is in memory. The address of the operand is the sum of the
address in the PC and the sign-extended 16-bit displacement integer in the extension word.
The value in the PC is the address of the extension word. The reference is a program space
reference and is only allowed for reads (refer to
4.2 Address Space Types
).
2.4.12 Program Counter Indirect with Index (8-Bit Displacement) Mode
This mode is similar to the address register indirect with index (8-bit displacement) mode
described in
2.4.7 Address Register Indirect with Index (8-Bit Displacement) Mode
, but
the PC is used as the base register. The operand is in memory. The address of the operand
is the sum of the address in the PC, the sign-extended displacement integer in the lower
eight bits of the extension word, and the sized, scaled, and sign-extended index operand.
The value in the PC is the address of the extension word. This reference is a program space
reference and is only allowed for reads. The user must include the displacement, the PC,
and the index register when specifying this addressing mode.
31 0
31 0
EA = (PC) + d
d ,PC)
111
010
GENERATION:
ASSEMBLER SYNTAX:
MODE:
REGISTER:
PROGRAM COUNTER:
MEMORY ADDRESS:
NUMBER OF EXTENSION WORDS: 1 OPERAND
+
SIGN EXTENDED 031 15
16
16
ADDRESS OF EXTENSION WORD
DISPLACEMENT: INTEGER
31 0
31 0
31 0
31 0
EA = (PC) + (Xn) + d
(d , PC,Xn. SIZE*SCALE)
111
011
+
OPERANDMEMORY ADDRESS:
NUMBER OF EXTENSION WORDS:
GENERATION:
ASSEMBLER SYNTAX:
MODE:
REGISTER:
PROGRAM COUNTER:
INTEGER
SIGN-EXTENDED VALUE
SCALE VALUE
+
X
DISPLACEMENT:
INDEX REGISTER
SCALE:
1
ADDRESS OF EXTENSION WORD
SIGN EXTENDED 7
8
8
70
Data Organization and Addressing Capabilities
MOTOROLA
MC68030 USER’S MANUAL
2-17
2.4.13 Program Counter Indirect with Index (Base Displacement) Mode
This mode is similar to the address register indirect with index (base displacement) mode
described in
2.4.8 Address Register Indirect with Index (Base Displacement) Mode
, but
the PC is used as the base register. It requires an index register indicator and an optional
16- or 32-bit sign-extended base displacement. The operand is in memory. The address of
the operand is the sum of the contents of the PC, the scaled contents of the sign-extended
index register, and the base displacement. The value of the PC is the address of the first
extension word. The reference is a program space reference and is only allowed for reads
(refer to
4.2 Address Space Types
).
In this mode, the PC, the index register, and the displacement are all optional. However, the
user must supply the assembler notation "ZPC'' (zero value is taken for the PC) to indicate
that the PC is not used. This allows the user to access the program space without using the
PC in calculating the effective address. The user can access the program space with a data
register indirect access by placing ZPC in the instruction and specifying a data register (Dn)
as the index register.
31 0
31 0
31 0
31 0
EA = (PC) + (Xn) + bd
(bd, PC, Xn. SIZE*SCALE)
111
011
+
OPERANDMEMORY ADDRESS:
NUMBER OF EXTENSION WORDS:
GENERATION:
ASSEMBLER SYNTAX:
MODE:
REGISTER:
PROGRAM COUNTER:
SIGN-EXTENDED VALUE
SCALE VALUE
+
X
BASE DISPLACEMENT:
INDEX REGISTER
SCALE:
1, 2 OR 3
ADDRESS OF EXTENSION WORD
SIGN-EXTENDED VALUE
07
Data Organization and Addressing Capabilities
2-18 MC68030 USER’S MANUAL MOTOROLA
2.4.14 Program Counter Memory Indirect Postindexed Mode
This mode is similar to the memory indirect postindexed mode described in 2.4.9 Memory
Indirect Postindexed Mode, but the PC is used as the base register. Both the operand and
operand address are in memory. The processor calculates an intermediate indirect memory
address by adding a base displacement (bd) to the PC contents. The processor accesses a
long word at that address and adds the scaled contents of the index register and the optional
outer displacement (od) to yield the effective address. The value of the PC used in the
calculation is the address of the first extension word. The reference is a program space
reference and is only allowed for reads (refer to 4.2 Address Space Types).
In the syntax for this mode, brackets enclose the values used to calculate the intermediate
memory address. All four user-specified values are optional. However, the user must supply
the assembler notation ZPC (zero value is taken for the PC) to indicate that the PC is not
used. This allows the user to access the program space without using the PC in calculating
the effective address. Both the base and outer displacements may be null, word, or long
word. When a displacement is omitted or an element is suppressed, its value is taken as
zero in the effective address calculation.
31 0
31 0
31 0
31 0
31 0
31 0
EFFECTIVE ADDRESS:
NUMBER OF EXTENSION WORDS: 1,2, 3, 4, OR 5
EA = (bd + PC) + Xn.SIZE*SCALE + od
([bd, PC], Xn.SIZE*SCALE,od)
111
011
GENERATION:
ASSEMBLER SYNTAX:
MODE:
REGISTER FIELD:
PROGRAM COUNTER:
SIGN-EXTENDED VALUE
SCALE VALUE
OPERAND
+
+
31 0
BASE DISPLACEMENT:
INDEX REGISTER:
MEMORY ADDRESS
INDIRECT MEMORY ADDRESS
VALUE AT INDIRECT MEMORY
ADDRESS IN PROGRAM SPACE
POINTS TO
SIGN-EXTENDED VALUE
SIGN-EXTENDED VALUE
+
X
OUTER DISPLACEMENT:
07
Data Organization and Addressing Capabilities
MOTOROLA MC68030 USER’S MANUAL 2-19
2.4.15 Program Counter Memory Indirect Preindexed Mode
This mode is similar to the memory indirect preindexed mode described in 2.4.10 Memory
Indirect Preindexed Mode, but the PC is used as the base register. Both the operand and
operand address are in memory. The processor calculates an intermediate indirect memory
address by adding the PC contents, a base displacement (bd), and the scaled contents of
an index register. The processor accesses a long word at that address and adds the optional
outer displacement (od) to yield the effective address. The value of the PC is the address of
the first extension word. The reference is a program space reference and is only allowed for
reads (refer to 4.2 Address Space Types).
In the syntax for this mode, brackets enclose the values used to calculate the intermediate
memory address. All four user-specified values are optional. However, the user must supply
the assembler notation ZPC (zero value is taken for the PC) to indicate that the PC is not
used. This allows the user to access the program space without using the PC in calculating
the effective address. Both the base and outer displacements may be null, word, or long
word. When a displacement is omitted or an element is suppressed, its value is taken as
zero in the effective address calculation.
31 0
31 0
31 0
31 0
31 0
31 0
31 0
EA = (bd + PC + Xn . SIZE * SCALE) + od
([bd, PC, Xn. SIZE*SCALE],od)
111
011
+
OPERANDEFFECTIVE ADDRESS:
NUMBER OF EXTENSION WORDS:
GENERATION:
ASSEMBLER SYNTAX:
MODE:
REGISTER FIELD:
PROGRAM COUNTER:
SIGN-EXTENDED VALUE
SCALE VALUE
+
X
BASE DISPLACEMENT:
INDEX REGISTER
1, 2, 3, 4 OR 5
ADDRESS OF EXTENSION WORD
SIGN-EXTENDED VALUE
INDIRECT MEMORY ADDRESS
POINTS TO
VALUE AT INDIRECT MEMORY
ADDRESS IN PROGRAM SPACE
SIGN-EXTENDED VALUE
+
OUTER DISPLACEMENT:
0
7
Data Organization and Addressing Capabilities
2-20 MC68030 USER’S MANUAL MOTOROLA
2.4.16 Absolute Short Addressing Mode
In this addressing mode, the operand is in memory, and the address of the operand is in the
extension word. The 16-bit address is sign-extended to 32 bits before it is used.
2.4.17 Absolute Long Addressing Mode
In this mode, the operand is in memory, and the address of the operand occupies the two
extension words following the instruction word in memory. The first extension word contains
the high-order part of the address; the low-order part of the address is the second extension
word.
31 0
31 0
OPERAND
MEMORY ADDRESSSIGN EXTENDED 15
GENERATION:
ASSEMBLER SYNTAX:
MODE:
REGISTER FIELD:
EXTENSION WORD:
EA GIVEN
(xxx).W
111
000
MEMORY ADDRESS:
NUMBER OF EXTENSION WORDS: 1
31 0
31 0
GENERATION:
ASSEMBLER SYNTAX:
MODE:
REGISTER FIELD:
FIRST EXTENSION WORD:
EA GIVEN
(xxx).L
111
001
CONCATENATION
OPERAND
SECOND EXTENSION WORD:
MEMORY ADDRESS:
NUMBER OF EXTENSION WORDS: 2
ADDRESS HIGH
ADDRESS LOW 0
0
15
15
Data Organization and Addressing Capabilities
MOTOROLA MC68030 USER’S MANUAL 2-21
2.4.18 Immediate Data
In this addressing mode, the operand is in one or two extension words:
Byte Operation
Operand is in the low-order byte of the extension word
Word Operation
Operand is in the extension word
Long-Word Operation
The high-order 16 bits of the operand are in the first extension word; the low-order 16
bits are in the second extension word.
Coprocessor instructions can support immediate data of any size. The instruction word is
followed by as many extension words as are required.
Generation: Operand given
Assembler Syntax: #xxx
Mode Field: 111
Register Field: 100
Number of Extension Words: 1 or 2, except for coprocessor instructions
Data Organization and Addressing Capabilities
2-22 MC68030 USER’S MANUAL MOTOROLA
2.5 EFFECTIVE ADDRESS ENCODING SUMMARY
Most of the addressing modes use one of the three formats shown in Figure 2–4. The single
effective address instruction is in the format of the instruction word. The encoding of the
mode field of this word selects the addressing mode. The register field contains the general
register number or a value that selects the addressing mode when the mode field contains
"111.'' Table 2–2 shows the encoding of these fields. Some indexed or indirect modes use
the instruction word followed by the brief format extension word. Other indexed or indirect
modes consist of the instruction word and the full format of extension words. The longest
instruction for the MC68030 contains 10 extension words. It is a MOVE instruction with full
format extension words for both source and destination effective addresses and with 32-bit
base displacements and 32-bit outer displacements for both addresses. However,
coprocessor instructions can have any number of extension words. Refer to the coprocessor
instruction formats in Section 10 Coprocessor Interface Description.
For effective addresses that use the full format, the index suppress (IS) bit and the index/
indirect selection (I/IS) field determine the type of indexing and indirection. Table 2–1 lists
the indexing and indirection operations corresponding to all combinations of IS and I/IS
values.
Table 2-1. IS–I/IS Memory Indirection Encodings
IS Index/Indirect Operation
0 000 No Memory Indirection
0 001 Indirect Preindexed with Null Outer Displacement
0 010 Indirect Preindexed with Word Outer Displacement
0 011 Indirect Preindexed with Long Outer Displacement
0 100 Reserved
0 101 Indirect Postindexed with Mull Outer Displacement
0 110 Indirect Postindexed with Word Outer Displacement
0 111 Indirect Postindexed with Long Outer Displacement
1 000 No Memory Indirection
1 001 Memory Indirect with Mull Outer Displacement
1 010 Memory Indirect with Word Outer Displacement
1 011 Memory Indirect with Long Outer Displacement
1 100–111 Reserved
Data Organization and Addressing Capabilities
MOTOROLA MC68030 USER’S MANUAL 2-23
Field Definition Field Definition
Instruction: BS Base Register Suppress:
Register General Register Number 0 = Base Register Added
Extensions: 1 = Base Register Suppressed
Register Index Register Number IS Index Suppress:
D/A Index Register Type 0 = Evaluate and Add Index
0 = Dn Operand
1 = An 1 = Suppress Index Operand
W/L Word/Long-Word Index Size BD SIZE Base Displacement Size:
0 = Sign-Extended Word 00 = Reserved
1 = Long Word 01 = Null Displacement
Scale Scale Factor 10 = Word Displacement
00 =1 11 Long Displacement
01 =2 I/IS Index/Indirect Selection
10 = 4 Indirect and Indexing Operand
11 = 8 Determined in Conjunction with
Bit 6, Index Suppress
Figure 2-4. Effective Address Specification Formats
Effective address modes are grouped according to the use of the mode. They can be
classified as follows:
Data A data addressing effective address mode is one that refers to data operands.
Memory A memory addressing effective address mode is one that refers to memory
operands.
Alterable An alterable addressing effective address mode is one that refers to alterable
(writable) operands.
Control A control addressing effective address mode is one that refers to memory
operands without an associated size.
Single Effective Address Instruction Format
15 14 13 12 11 10 9 8 7 6 5 0
X XXXXXXXXX EFFECTIVE ADDRESS
MODE REGISTER
Brief Format Extension Word
15 14 12 11 10 9 8 7 0
D/A REGISTER W/L SCALE 0 DISPLACEMENT
Full Format Extension Word(s)
15 14 12111098765432 0
D/A REGISTER W/L SCALE 1 BS IS BD SIZE 0 I/IS
BASE DISPLACEMENT (0, 1, OR 2 WORDS)
OUTER DISPLACEMENT (0, 1, OR 2 WORDS)
Data Organization and Addressing Capabilities
2-24 MC68030 USER’S MANUAL MOTOROLA
Table 2–2 shows the categories to which each of the effective addressing modes belong.
These categories are sometimes combined, forming new categories that are more
restrictive. Two combined classifications are alterable memory or data alterable. The former
refers to those addressing modes that are both alterable and memory addresses, and the
latter refers to addressing modes that are both data and alterable.
2.6 PROGRAMMER`S VIEW OF ADDRESSING MODES
Extensions to the indexed addressing modes, indirection, and full 32-bit displacements
provide additional programming capabilities for both the MC68020 and the MC68030. This
section describes addressing techniques that exploit these capabilities and summarizes the
addressing modes from a programming point of view.
Addressing Modes Mode Register Data Memory Control Alterable Assembler
Syntax
Data Register Direct 000 reg. no. X — — X Dn
Address Register Direct 001 reg. no. — — — X An
Address Register Indirect
Address Register Indirect
with Postincrement
Address Register Indirect
with Predecrement
Address Register Indirect
with Displacement
010
011
100
101
reg. no
reg. no.
reg. no.
reg. no.
X
X
X
X
X
X
X
X
X
—
—
X
X
X
X
X
(An)
(An)+
-(An)
(d16,An)
Address Register Indirect with
Index (8-Bit Displacement)
Address Register Indirect with
Index (Base Displacement)
Memory Indirect Postindexed
Memory Indirect Preindexed
110
110
110
110
reg. no.
reg. no.
reg. no
reg. no.
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
(d8,An,Xn)
(bd,An,Xn)
([bd,An],Xn,od)
([bd,An,Xn],od)
Absolute Short
Absolute Long 111
111 000
001 X
XX
XX
XX
X(xxx).W
(xxx).L
Program Counter Indirect
with Displacement
Program Counter Indirect
with Index (8-Bit) Displacement
Program Counter Indirect
with Index (Base Displacement)
PC Memory Indirect
Postindexed
PC Memory Indirect
Preindexed
111
111
111
111
111
010
011
011
011
011
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
—
—
—
—
—
(d16,PC)
(d8,PC,Xn)
(bd,PC,Xn)
([bd,PC],Xn,od)
([bd,PC,Xn],od)
Immediate 111 100 X X — — #〈data〉
Data Organization and Addressing Capabilities
MOTOROLA MC68030 USER’S MANUAL 2-25
Several of the addressing techniques described in this section use data registers and
address registers interchangeably. While the MC68030 provides this capability, its
performance has been optimized for addressing with address registers. The performance of
a program that uses address registers in address calculations is superior to that of a
program that similarly uses data registers.The performance has been optimized for
addressing registers in address calculations is superior to that of a program that similarly
uses data registers. The specification of addresses with data registers should be used
sparingly (if at all), particularly in programs that require maximum performance.
2.6.1 Addressing Capabilities
In both the MC68020 and the MC68030, setting the base register suppress (BS) bit in the
full format extension word (see Figure 2–4) suppresses use of the base address register in
calculating the effective address. This allows any index register to be used in place of the
base register. Since any of the data registers can be index registers, this provides a data
register indirect form (Dn). The mode could be called register indirect (Rn) since either a
data register or an address register can be used. This addressing mode is an extension to
the M68000 Family because the MC68030 and MC68020 can use both the data registers
and the address registers to address memory. The capabilities of specifying the size and
scale of an index register (Xn.SIZE*SCALE) in these modes provides additional addressing
flexibility. Using the SIZE parameter, either the entire contents of the index register can be
used, or the least significant word can be sign-extended to provide a 32-bit index value (refer
to Figure 2–5).
Figure 2-5. Using SIZE in the Index Selection
D1.L
D1.W
D1
D1
31
16 1531 0
0
USED IN ADDRESS CALCULATION
Data Organization and Addressing Capabilities
2-26 MC68030 USER’S MANUAL MOTOROLA
For both the MC68020 and the MC68030, the register indirect modes can be extended
further. Since displacements can be 32 bits wide, they can represent absolute addresses or
the results of expressions that contain absolute addresses. This allows the general register
indirect form to be (bd,Rn) or (bd,An,Rn) when the base register is not suppressed. Thus,
an absolute address can be directly indexed by one or two registers (refer to Figure 2–6).
Scaling provides an optional shifting of the value in an index register to the left by zero, one,
two, or three bits before using it in the effective address allocation (the actual value in the
index register remains unchanged). This is equivalent to multiplying the register by one, two,
four, or eight or direct subscripting into an array of elements of corresponding size using an
arithmetic value residing in any of the 16 general registers. Scaling does not add to the
effective address calculation time. However, when combined with the appropriate derived
modes, it produces additional capabilities. Arrayed structures can be addressed absolutely
and then subscripted, (bd,Rn*scale). Another variation that can be derived is (An,Rn*scale).
In the first case, the array address is the sum of the contents of a register and a
displacement, as shown in Figure 2–7. In the second example. An contains the address of
an array and Rn contains a subscript.
Figure 2-6. Using Absolute Address with Indexes
An
Rn
bd
SYNTAX (bd,An,Rn)
Data Organization and Addressing Capabilities
MOTOROLA MC68030 USER’S MANUAL 2-27
Figure 2-7. Addressing Array Items
A6 = 1
2
3
4
SIMPLE ARRAY
(SCALE = 1) RECORD OF 2 WORDS
(SCALE = 2)
A6 = 1
2
2
A6 = 1
2
A6 = 1
15 015 0
SYNTAX: MOVE.W (A5, A6.L*SCALE),(A7)
WHERE:
A5 = ADDRESS OF ARRAY STRUCTURE
A6 = INDEX NUMBER OF ARRAY ITEM
A7 = STACK POINTER
RECORD OF 4 WORDS
(SCALE = 4) RECORD OF 8 WORDS
(SCALE = 8)
NOTE: Regardless of array structure, software increments
index by the appropriate amount to point to next record.
15 0 15 0
Data Organization and Addressing Capabilities
2-28 MC68030 USER’S MANUAL MOTOROLA
The memory indirect addressing modes use a long-word pointer in memory to access an
operand. Any of the modes previously described can be used to address the memory
pointer. Because the base and index registers can both be suppressed, the displacement
acts as an absolute address, providing indirect absolute memory addressing (refer to Figure
2–8).
The outer displacement (od) available in the memory indirect modes is added to the pointer
in memory. The syntax for these modes is ([bd,An],Xn,od) and ([bd,An,Xn],od). When the
pointer is the address of a structure in memory and the outer displacement is the offset of
an item in the structure, the memory indirect modes can access the item efficiently (refer to
Figure 2–9).
Memory indirect addressing modes are used with a base displacement in five basic forms:
1. [bd,An] — Indirect, suppressed index register
2. ([bd,An,Xn]) — Preindexed indirect
3. ([bd,An],Xn) — Postindexed indirect
4. ([bd,An,Xn],od) — Preindexed indirect with outer displacement
5. ([bd,An],Xn,od) — Postindexed indirect with outer displacement
The indirect, suppressed index register mode (see Figure 2–10) uses the contents of
register An as an index to the pointer located at the address specified by the displacement.
The actual data item is at the address in the selected pointer.
The preindexed indirect mode (see Figure 2–11) uses the contents of An as an index to the
pointer list structure at the displacement. Register Xn is the index to the pointer, which
contains the address of the data item.
Figure 2-8. Using Indirect Absolute Memory Addressing
POINTER DATA ITEM
bd
SYNTAX: ([bd])
Data Organization and Addressing Capabilities
MOTOROLA MC68030 USER’S MANUAL 2-29
Figure 2-9. Accessing an Item in a Structure Using a Pointer
Figure 2-10. Indirect Addressing, Suppressed Index Register
POINTER
DATA ITEM
An
od
MEMORY STRUCTURE
SYNTAX: ([An],od)
POINTER DATA ITEM
bd
POINTER LIST
SYNTAX: ([bd,An])
An
Data Organization and Addressing Capabilities
2-30 MC68030 USER’S MANUAL MOTOROLA
Figure 2-11. Preindexed Indirect Addressing
POINTER
DATA ITEM
bd
POINTER LIST
SYNTAX: ([bd,An,Xn])
Xn
An
Data Organization and Addressing Capabilities
MOTOROLA MC68030 USER’S MANUAL 2-31
The postindexed indirect mode (see Figure 2–12) uses the contents of An as an index to the
pointer list at the displacement. Register Xn is used as an index to the structure of data items
located at the address specified by the pointer. Figure 2–13 shows the preindexed indirect
addressing with outer displacement mode.
Figure 2-12. Postindexed Indirect Addressing
Figure 2-13. Preindexed Indirect Addressing with Outer Displacement
POINTER DATA ITEM
bd
POINTER LIST
SYNTAX: ([bd,An],Xn)
Xn
An
POSTINDEXED STRUCTURE
POINTER DATA ITEM
bd
POINTER LIST
SYNTAX: ([bd,An,Xn],od)
od
An
Xn
STRUCTURE
Data Organization and Addressing Capabilities
2-32 MC68030 USER’S MANUAL MOTOROLA
The postindexed indirect mode with outer displacement (see Figure 2–14) uses the contents
of An as an index to the pointer list at the displacement. Register Xn is used as an index to
the structure of data structures at the address in the pointer. The outer displacement (od) is
the displacement of the data item within the selected data structure.
2.6.2 General Addressing Mode Summary
The addressing modes described in the previous section are derived from specific
combinations of options in the indexing mode or a selection of two alternate addressing
modes. For example, the addressing mode called register indirect (Rn) assembles as the
address register indirect if the register is an address register. If Rn is a data register, the
assembler uses the address register indirect with index mode using the data register as the
indirect register and suppresses the address register by setting the base suppress bit in the
effective address specification. Assigning an address register as Rn provides higher
performance than using a data register as Rn. Another case is (bd,An), which selects an
addressing mode depending on the size of the displacement. If the displacement is 16 bits
or less, the address register indirect with displacement mode (d16,An) is used. When a 32-
bit displacement is required, the address register indirect with index (bd,An,Xn) is used with
the index register suppressed.
Figure 2-14. Postindexed Indirect Addressing with Outer Displacement
POINTER DATA ITEM
bd
POINTER LIST
SYNTAX: ([bd,An],Xn,od)
od
An
POSTINDEXED STRUCTURE
WITH OUTER DISPLACEMENT
Xn
Data Organization and Addressing Capabilities
MOTOROLA MC68030 USER’S MANUAL 2-33
It is useful to examine the derived addressing modes available to a programmer (without
regard to the MC68030 effective addressing mode actually encoded) because the
programmer need not be concerned about these decisions. The assembler can choose the
more efficient addressing mode to encode.
In the list of derived addressing modes that follows, common programming terms are used.
The following definitions apply:
pointer — long-Word value in a register or in memory which represents an
address.
base — A pointer combined with a displacement to represent an address.
index — A constant or variable value added into an effective address calcula-
tion. A constant index is a displacement. A variable index is always
represented by a register containing the value.
disp — Displacement, a constant index.
subscript — The use of any of the data or address registers as a variable index
subscript into arrays of items 1, 2, 4 or 8 bytes in size.
relative — An address calculated from the program counter contents. The
address is position independent and is in program space. All other
addresses but psaddr are in data space.
addr — An absolute address.
psaddr — An absolute address in program space. All other addresses but PC
relative are in data space.
preindexed — All modes from absolute address through program counter relative.
postindexed— Any of the following modes:
addr — Absolute address in data space
psaddr,ZPC — Absolute address in program space
An — Register pointer with constant displacement
disp.An — Register pointer with constant displacement
addr,An — Absolute address with single variable name
disp,Pc — Simple PC relative
The addressing modes defined in programming terms, which are derivations of the
addressing modes provided by the MC68030 architecture, are as follows:
Immediate Data — #data:
The data is a constant located in the instruction stream.
Register Direct — Rn:
The contents of a register contain the operand.
Scanning Modes:
(An)+
Data Organization and Addressing Capabilities
2-34 MC68030 USER’S MANUAL MOTOROLA
Address register pointer automatically incremented after use.
– (An)
Address register pointer automatically decremented before use.
Absolute Address:
(addr)
Absolute address in data space.
(psaddr,ZPC)
Absolute address in program space. Symbol ZPC suppresses the PC,
but retains PC relative mode to directly access the program space.
Register Pointer:
(Rn)
Register as a pointer.
(disp,Rn)
Register as a pointer with constant index (or base address).
Indexing
(An,Rn)
Register pointer An with variable index Rn.
(disp,An,Rn)
Register pointer with constant and variable index (or a base address
with a variable index).
(addr,Rn)
Absolute address with two variable indexes.
Subscripting:
(An,Rn*scale)
Address register pointer subscript.
(disp,An,Rn*scale)
Address register pointer subscript with constant displacement
(or base address with subscript).
(addr,Rn*scale)
Absolute address with subscript.
(addr,An,Rn*scale)
Absolute address subscript with variable index.
Program Relative:
Data Organization and Addressing Capabilities
MOTOROLA MC68030 USER’S MANUAL 2-35
(disp,PC)
Simple PC relative.
(disp,PC,Rn)
PC relative with variable index.
(disp,PC,Rn*scale)
PC relative with subscript.
Memory Pointer:
([preindexed])
Memory pointer directly to data operand.
([preindexed],disp)
Memory pointer as base with displacement to data operand.
([postindexed],Rn)
Memory pointer with variable index.
([postindexed],disp,Rn)
Memory pointer with constant and variable index.
([postindexed],Rn*scale)
Memory pointer subscripted.
([postindexed],disp,Rn*scale)
Memory pointer subscripted with constant index.
Data Organization and Addressing Capabilities
2-36 MC68030 USER’S MANUAL MOTOROLA
2.7 M68000 FAMILY ADDRESSING COMPATIBILITY
Programs can be easily transported from one member of the M68000 Family to another in
an upward compatible fashion. The user object code of each early member of the family is
upward compatible with newer members and can be executed on the newer microprocessor
without change. The address extension word(s) are encoded with the information that allows
the MC68020/MC68030 to distinguish the new address extension words for the early
MC68000/MC68008/MC68010 microprocessors and for the newer 32-bit MC68020/
MC68030 microprocessors are shown in Figure 2–15. Notice the encoding for SCALE used
by the MC68020/MC68030 is a compatible extension of the M68000 architecture. A value
of zero for SCALE is the same encoding for both extension words; hence, software that uses
this encoding is both upward and downward compatible across all processors in the product
line. However, the other values of SCALE are not found in both extension formats; thus,
while software can be easily migrated in an upward compatible direction, only nonscaled
addressing is supported in a downward fashion. If the MC68000 were to execute an
instruction that encoded a scaling factor, the scaling factor would be ignored and not access
the desired memory address. The earlier microprocessors have no knowledge of the
extension word formats implemented by newer processors; while they do detect illegal
instructions, they do not decode invalid encodings of the extension words as exceptions.
2.8 OTHER DATA STRUCTURES
Stacks and queues are widely used data structures. The MC68030 implements a system
stack and also provides instructions that support the use of user stacks and queues.
2.8.1 System Stack
Address register seven (A7) is used as the system stack pointer (SP). Any of the three
system stack registers is active at any one time. The M and S bits of the status register
determine which stack pointer is used. When S = 0 indicating user mode (user privilege
level), the user stack pointer (USP) is the active system stack pointer, and the master and
interrupt stack pointers cannot be referenced. When S = 1 indicating supervisor mode (at
supervisor privilege level) and M = 1, the master stack pointer (MSP) is the active system
stack pointer. When S = 1 and M = 0, the interrupt stack pointer (ISP) is the active system
stack pointer. This mode is the MC68030 default mode after reset and corresponds to the
MC68000, MC68008, and MC68010 supervisor mode. The term supervisor stack pointer
(SSP) refers to the master or interrupt stack pointers, depending on the state of the M bit.
When M = 1, the term SSP (or A7) refers to the MSP address register. When M = 0, the term
is implicitly referenced by all instructions that use the system stack. Each system stack fills
from high to low memory.
Data Organization and Addressing Capabilities
MOTOROLA MC68030 USER’S MANUAL 2-37
A subroutine call saves the program counter on the active system stack, and the return
restores it from the active system stack. During the processing of traps and interrupts, both
the program counter and the status register are saved on the supervisor stack (either master
or interrupt). Thus, the execution of supervisor code is independent of user code and the
condition of the user stack; conversely, user programs use the user stack pointer
independently of supervisor stack requirements.
To keep data on the system stack aligned for maximum efficiency, the active stack pointer
is automatically decremented or incremented by two for all byte-sized operands moved to
or from the stack. In long-word-organized memory, aligning the stack pointer on a long-word
address signed significantly increases the efficiency of stacking exception frames,
subroutine calls and returns, and other stacking operations.
(UNABLE TO LOCATE ART. MUST BE RECREATED.)
Figure 2-15. M68000 Family Address Extension Words
Data Organization and Addressing Capabilities
2-38 MC68030 USER’S MANUAL MOTOROLA
2.8.2 User Program Stacks
The user can implement stacks with the address register indirect with postincrement and
predecrement addressing modes. With address register An (n = 0–6), the user can
implement a stack that is filled wither from high to low memory or from low to high memory.
Important considerations are:
• Use the predecrement mode to decrement the register before its contents are used as
the pointer to the stack.
• Use the postincrement mode to increment the register after its contents are used as the
pointer to the stack.
• Maintain the stack pointer correctly when byte, word, and long-word items are mixed in
these stacks.
To implement stack growth from high to low memory, use:
–(An) to push data on the stack,
(An)+ to pull data from the stack.
For this type of stack, after either a push or a pull operation, register An points to the top item
on the stack. This is illustrated as:
To implement stack growth from low to high memory, use:
(An)+ to push data on the stack,
–An to pull data from the stack.
An LOW MEMORY
(FREE)
TOP OF STACK
BOTTOM OF STACK
HIGH MEMORY
Data Organization and Addressing Capabilities
MOTOROLA MC68030 USER’S MANUAL 2-39
In this case, after either a push or pull operation, register An points to the next available
space on the stack. This is illustrated as:
2.8.3 Queues
The user can implement queues with the address register indirect with postincrement or
predecrement addressing modes. Using a pair of address registers (who of A0–A6), the user
can implement a queue which is filled either from high to low memory or from low to high
memory. Two registers are used because queues are pushed from one end and pulled from
the other. One register, An, contains the "put'' pointer; the other, Am, the "get'' pointer.
To implement growth of the queue from low to high memory, use:
(An)+ to put data into the queue,
(Am)+ to get data from the queue.
After a "put'' operation, the "put'' address register points to the next available space in the
queue, and the unchanged "get'' address register points to the next item to be removed from
the queue. After a "get'' operation, the "get'' address register points to the next item to be
removed from the queue, and the unchanged "put'' address register points to the next
available space in the queue. This is illustrated as:
To implement the queue as a circular buffer, the relevant address register should be
checked and adjusted, if necessary, before performing the "put'' or "get'' operation. The
address register is adjusted by subtracting the buffer length (in bytes) from the register.
LOW MEMORY
TOP OF STACK
HIGH MEMORY
An
BOTTOM OF STACK
(FREE)
GET (Am) +
LOW MEMORY
(FREE)
HIGH MEMORY
LAST GET (FREE)
LAST PUT
NEXT GET
PUT (An) +
Data Organization and Addressing Capabilities
2-40 MC68030 USER’S MANUAL MOTOROLA
To implement growth of the queue from high to low memory, use:
–(An) to put data into the queue,
–(Am) to get data from the queue.
After a "put'' operation, the "put'' address register points to the last item place din the queue,
and the unchanged "get'' address register points to the last item removed from the queue.
After a "get'' operation, the "get'' address register points to the last item removed from the
queue, and the unchanged "put'' address register points to the last item placed in the queue.
This is illustrated as:
To implement the queue as a circular buffer, the "get'' or "put'' operation should be
performed first, and then the relevant address register should be checkout and adjusted, if
necessary. The address register is adjusted by adding the buffer length (in bytes) to the
register contents.
LOW MEMORY
(FREE)
HIGH MEMORY
LAST GET (FREE)
LAST PUT
NEXT GET
PUT - (An)
GET - (Am)
MOTOROLA
MC68030 USER’S MANUAL
3-1
SECTION 3
INSTRUCTION SET SUMMARY
This section briefly describes the MC68030 instruction set. Refer to the MC68000PM/AD,
MC68000 Programmer's Reference Manual
, for complete details on the MC68030
instruction set.
The following paragraphs include descriptions of the instruction format and the operands
used by instructions, followed by a summary of the instruction set. The integer condition
codes and floating-point details are discussed. Programming examples for selected
instructions are also presented.
3.1 INSTRUCTION FORMAT
All MC68030 instructions consist of at least one word; some have as many as 11 words (see
Figure 3–1). The first word of the instruction, called the operation word, specifies the length
of the instruction and the operation to be performed. The remaining words, called extension
words, further specify the instruction and operands. These words may be floating-point
command words, conditional predicates, immediate operands, extensions to the effective
address mode specified in the operation word, branch displacements, bit number or bit field
specifications, special register specifications, trap operands, pack/unpack constants, or
argument counts.
Figure 3-1. Instruction Word General Format
15 0
OPERATION WORD(ONE WORD,
SPECIFIES OPERATION AND MODES)
SPECIAL OPERAND SPECIFIERS
(IF ANY, ONE OR TWO WORDS)
IMMEDIATE OPERAND OR SOURCE EFFECTIVE ADDRESS EXTENSION(
IF ANY, ONE TO SIX WORDS)
DESTINATION EFFECTIVE ADDRESS EXTENSION
(IF ANY, ONE TO SIX WORDS)
Instruction Set Summary
3-2
MC68030 USER’S MANUAL
MOTOROLA
Besides the operation code, which specifies the function to be performed, an instruction
defines the location of every operand for the function. Instructions specify an operand
location in one of three ways:
1. Register Specification — A register field of the instruction contains the number of the
register.
2. Effective Address — An effective address field of the instruction contains address
mode information.
3. Implicit Reference — The definition of an instruction implies the use of specific regis-
ters.
The register field within an instruction specifies the register to be used. Other fields within
the instruction specify whether the register selected is an address or data register and how
the register is to be used.
Section 1 Introduction
contains register information.
Effective address information includes the registers, displacements, and absolute
addresses for the effective address mode.
Section 2 Data Organization and Addressing
Capabilities
describes the effective address modes in detail.
Certain instructions operate on specific registers. These instructions imply the required
registers.
3.2 INSTRUCTION SUMMARY
The instructions form a set of tools to perform the following operations:
Each instruction type is described in detail in the following paragraphs
Data Movement
Integer Arithmetic
Logical
Shift and Rotate
Bit Manipulation
Bit Field Manipulation
Binary-Coded Decimal Arithmetic
Program Control
System Control
Multiprocessor Communications
Instruction Set Summary
MOTOROLA
MC68030 USER’S MANUAL
3-3
The following notations are used in this section. In the operand syntax statements of the
instruction definitions, the operand on the right is the destination operand.
An = any address register, A7–A0
Dn = any data register, D7–D0
Rn = any address or data register
CCR = condition code register (lower byte of status register)
cc = condition codes from CCR
SR = status register
SP = active stack pointer
USP = user stack pointer
ISP = supervisor/interrupt stack pointer
MSP = supervisor/master stack pointer
SSP = supervisor (master or interrupt) stack pointer
DFC = destination function code register
SFC = source function code register
Rc = control register (VBR, SFC, DFC, CACR)
MRc = MMU control register (SRP, URP, TC, DTT0, DTT1, ITT0,
ITT1, MMUSR)
MMUSR = MMU status register
B, W, L = specifies a signed integer data type (twos complement) of
byte, word, or long word
S = single-precision real data format (32 bits)
D = double-precision real data format (64 bits)
X = extended-precision real data format (96 bits, 16 bits unused)
P = packed BCD real data format (96 bits, 12 bytes)
FPm, FPn = any floating-point data register, FP7-FP0
PFcr = floating-point system control register (FPCR, FPSR, or
FPIAR)
k = a twos-complement signed integer (–64 to +17) that specifies
the format of a number to be stored in the packed BCD format
d= displacement; d
16
is a 16-bit displacement
〈
ea
〉
= effective address
list = list of registers, for example D3 — D0
#
〈
data
〉
= immediate data; a literal integer
{offset:width} = bit field selection
label = assemble program label
[m] = bit m of an operand
[m:n] = bits m through n of operand
Instruction Set Summary
3-4
MC68030 USER’S MANUAL
MOTOROLA
3.2.1 Data Movement Instructions
The MOVE instructions with their associated addressing modes are the basic means of
transferring and storing addresses and data. MOVE instructions transfer byte, word, and
long-word operands from memory to memory, memory to register, register to memory, and
register to register. Address movement instructions (MOVE or MOVEA) transfer word and
long-word operands and ensure that only valid address manipulations are executed. In
addition to the general MOVE instructions, there are several special data movement
instructions: move multiple registers (MOVEM), move peripheral data (MOVEP), move
quick (MOVEQ), exchange registers (EXG), load effective address (LEA), push effective
address (PEA), link stack (LINK), and unlink stack (UNLK).
X = extend (X) bit in CCR
N = negative (N) bit in CCR
Z = Zero (Z) bit in CCR
V = overflow (V) bit in CCR
C = carry (C) bit in CCR
+ = arithmetic addition or postincrement indicator
– = arithmetic subtraction or predecrement indicator
x = arithmetic multiplication
÷
= arithmetic division or conjunction symbol
~ = invert; operand is logically complemented
Λ
= logical AND
V = logical OR
⊕
= logical exclusive OR
Dc = data register, D7-D0 used during compare
Du = data register, D7-D0 used during update
Dr, Dq = data registers, remainder or quotient of divide
Dh, Dl = data registers, high or lo
•
order 32 bits of product
MSW = most significant word
LSW = least significant word
MSB = most significant bit
FC = function code
{R/W} = read or write indicator
[An] = address extensions
Instruction Set Summary
MOTOROLA
MC68030 USER’S MANUAL
3-5
Table 3–1 is a summary of the integer and floating-point data movement operations.
3.2.2 Integer Arithmetic Instructions
The integer arithmetic operations include the four basic operations of add (ADD), subtract
(SUB), multiply (MUL), and divide (DIV) as well as arithmetic compare (CMP, CMPM,
CMP2), clear (CLR), and negate (NEG). The instruction set includes ADD, CMP, and SUB
instructions for both address and data operations with all operand sizes valid for data
operations. Address operands consist of 16 or 32 bits. The clear and negate instructions
apply to all sizes of data operands.
Signed and unsigned MUL and DIV instructions include:
• Word multiply to produce a long-word product
• Long-word multiply to produce and long-word or quad-word product
• Division of a long word divided by a word divisor (word quotient and word remainder)
• Division of a long word or quad word dividend by a long-word divisor (long-word quo-
tient and long-word remainder)
A set of extended instructions provides multiprecision and mixed-size arithmetic. These
instructions are add extended (ADDX), subtract extended (SUBX), sign extended (EXT),
and negate binary with extend (NEGX). Refer to Table 3–2 for a summary of the integer
arithmetic operations.
Table 3-1. Data Movement Operations
Instruction Operand Syntax Operand Size Operation
EXG Rn,Rn 32 Rn
↔
Rn
LEA
〈
ea
〉
,An 32
〈
ea
〉
→
An
LINK An,#
〈
d
〉
16, 32 Sp - 4
→
SP; An
→
(SP); SP
→
An, SP + D
→
SP
MOVE
MOVEA
〈
ea
〉
,
〈
ea
〉
,An 8, 16, 32
16, 32
→
32 source
→
destination
MOVEM list,
〈
ea
〉
,list 16, 32
16, 32
→
32 listed registers
→
destination
source
→
listed registers
MOVEP
Dn,(d
16
,An)
(d
16
,An),Dn
16, 32
Dn[31:24]
→
(An + d); Dn[23:16]
→
An + d + 2);
Dn[15:8]
→
(An + d + 4); Dn[7:0]
→
(An + d + 6)
(An + d)
→
Dn[31:24]; (An + d + 2)
→
Dn[23:16];
(An + d + 4)
→
Dn[15:8]; (An + d + 6)
→
Dn[7:0]
MOVEQ #
〈
data
〉
,Dn 8
→
32 immediate data
→
destination
PEA
〈
ea
〉
32 SP — 4
→
SP;
〈
ea
〉
→
(SP)
UNLK An 32 An
→
SP; (SP)
→
An; SP + 4
→
SP
Instruction Set Summary
3-6
MC68030 USER’S MANUAL
MOTOROLA
3.2.3 Logical Instructions
The logical operation instructions (AND, OR, EOR, and NOT) perform logical operations
with all sizes of integer data operands. A similar set of immediate instructions (ANDI, ORI,
and EORI) provide these logical operations with all sizes of immediate data. The TST
instruction compares the operand with zero arithmetically, placing the result in the condition
code register. Table 3–3 summarizes the logical operations.
Table 3-2. Integer Arithmetic Operations
Instruction Operand Syntax Operand Size Operation
ADD
ADDA
Dn,
〈
ea
〉
〈
ea
〉
,Dn
〈
ea
〉
,An
8, 16, 32
8, 16, 32
16, 32
source + destination
→
destination
ADDI
ADDQ #
〈
data
〉
,
〈
ea
〉
#
〈
data
〉
,
〈
ea
〉
8, 16, 32
8, 16, 32 immediate data + destination
→
destination
ADDX Dn,Dn
–(An),–(An) 8, 16, 32
8, 16, 32 source + destination + X
→
destination
CLR
〈
ea
〉
8, 16, 32 0
→
destination
CMP
CMPA
〈
ea
〉
,Dn
〈
ea
〉
,An 8, 16, 32
16, 32
destination - source
CMPI #
〈
data
〉
,
〈
ea
〉
8, 16, 32 destination - immediate data
CMPM (An) +,(An) + 8, 16, 32 destination - source
CMP2
〈
ea
〉
,Rn 8, 16, 32 lower bound < = Rn < = upper bound
DIVS/DIVU
DIVSL/DIVUL
〈
ea〉,Dn
〈ea〉,Dr:Dq
〈ea〉,Dq
〈ea〉,Dr:Dq
32/16 → 16:16
64/32 → 32:32
32/32 → 32
32/32 → 32:32
destination/source → destination (signed or unsigned)
EXT
EXTB
Dn
Dn
Dn
8 → 16
16 → 32
8 → 32
sign-extended destination → destination
MULS/MULU 〈ea〉,Dn
〈ea〉,Dl
(ea〉,Dh:Dl
16x16 → 32
32x32 → 32
32x32 → 64
source y destination → destination (signed or unsigned)
NEG 〈ea〉 8, 16, 32 0 - destination → destination
NEGX 〈ea〉 8, 16, 32 0 - destination - X → destination
SUB
SUBA
〈ea〉,Dn
Dn,〈ea〉
〈ea〉,An
8, 16, 32
8, 16, 32
16, 32
destination = source → destination
SUBI
SUBQ #〈data〉,〈ea〉
#〈data〉,〈ea〉 8, 16, 32
8, 16, 32 destination - immediate data → destination
SUBX Dn,Dn
–(An),–(An) 8, 16, 32
8, 16, 32 destination - source — X → destination
Instruction Set Summary
MOTOROLA MC68030 USER’S MANUAL 3-7
3.2.4 Shift and Rotate Instructions
The arithmetic shift instructions (ASR and ASL) and logical shift instructions (LSR and LSL)
provide shift operations in both directions. The ROR, ROL, ROXR, and ROXL instructions
perform rotate (circular shift) operations, with and without the extend bit. All shift and rotate
operations can be performed on either registers or memory.
Register shift and rotate operations shift all operand sizes. The shift count may be specified
in the instruction operation word (to shift from 1–8 places) or in a register (modulo 64 shift
count).
Memory shift and rotate operations shift word-length operands one bit position only. The
SWAP instruction exchanges the 16-bit halves of a register. Performance of shift/rotate
instructions is enhanced so that use of the ROR and ROL instructions with a shift count of
eight allows fast byte swapping. Table 3–4 is a summary of the shift and rotate operations.
Table 3-3. Logical Operations
Instruction Operand Syntax Operand Size Operation
AND 〈ea〉,Dn
Dn,〈ea〉 8, 16, 32
8, 16, 32 source Λ destination → destination
ANDI #〈data〉,〈ea〉 8, 16, 32 immediate data Λ destination → destination
EOR Dn,〈data〉,〈ea〉 8, 16, 32 source ⊕ destination → destination
EORI #〈data〉,〈ea〉 8, 16, 32 immediate data x destination → destination
NOT 〈ea〉 8, 16, 32 ∼ destination → destination
OR 〈ea〉,Dn
Dn,〈ea〉 8, 16, 32
8, 16, 32 source V destination → destination
ORI #〈data〉,〈ea〉 8, 16, 32 immediate data V destination → destination
TST #〈ea〉 8, 16, 32 source — 0 to set condition codes
Instruction Set Summary
3-8 MC68030 USER’S MANUAL MOTOROLA
Table 3-4. Shift and Rotate Operations.
3.2.5 Bit Manipulation Instructions
Bit manipulation operations are accomplished using the following instructions: bit test
(BTST), bit test and set (BSET), bit test and clear (BCLR), and bit test and change (BCHG).
All bit manipulation operations can be performed on either registers or memory. The bit
number is specified as immediate data or in a data register. Register operands are 32 bits
long, and memory operands are 8 bits long. In Table 3–5, the summary of the bit
manipulation operations, Z refers to bit 2, the zero bit of the status register.
X/C
X/C 0
X/C0
C
C
XC
X/C 0
X C
MSW LSW
Instruction Set Summary
MOTOROLA MC68030 USER’S MANUAL 3-9
3.2.6 Bit Field Operations
The MC68030 supports variable-length bit field operations on fields of up to 32 bits. The bit
field insert (BFINS) instruction inserts a value into a bit field. Bit field extract unsigned
(BFEXTU) and bit field extract signed (BFEXTS) extract a value from the field. Bit field find
first one (BFFFO) finds the first bit that is set in a bit field. Also included are instructions that
are analogous to the bit manipulation operations; bit field test (BFTST), bit field test and set
(BFSET), bit field test and clear (BFCLR), and bit field test and change (BFCHG). Table 3–
6 is a summary of the bit field operations.
NOTE: All bit field instructions set the N and Z bits as shown for BFTST before performing the specified operation.
Table 3-5. Bit Manipulation Operations
Instruction Operand Syntax Operand Size Operation
BCHG Dn,〈ea〉
#〈data〉,ea 8, 32
8, 32 ∼ (〈bit number〉 of destination) → Z → bit of destination
BCLR Dn,〈ea〉
#〈data〉,ea 8, 32
8, 32 ∼ (〈bit number〉 of destination) → Z;
— 0 → bit of destination
BSET Dn,〈ea〉
#〈data〉,〈ea〉 8, 32
8, 32 ∼ (〈bit number〉 of destination) → Z;
— 1 → bit of destination
BTST Dn,〈ea〉
#〈data〉,ea 8, 32
8, 32 ∼ (〈bit number〉 of destination) → Z
Table 3-6. Bit Field Operations
Instruction Operand Syntax Operand Size Operation
BFCHG 〈ea〉 {offset:width} 1 — 32 ∼ Field → Field
BFCLR 〈ea〉 {offset:width} 1 — 32 0's → Field
BFEXTS 〈ea〉 {offset:width},Dn 1—32 Field → Dn; Sign Extended
BFEXTU 〈ea〉 {offset:width},Dn 1 — 32 Field → Dn; Zero Extended
BFFFO 〈ea〉 {offset:width},Dn 1 — 32 Scan for first bit set in field; offset → Dn
BFINS Dn,〈ea〉 {offset:width} 1 — 32 Dn → Field
BFSET 〈ea〉 {offset:width} 1 — 32 1's → Field
BFTST 〈ea〉 {offset:width} 1 — 32 Field MSB → N; ∼ (OR of all bits in field) → Z
Instruction Set Summary
3-10 MC68030 USER’S MANUAL MOTOROLA
3.2.7 Binary–coded Decimal Instructions
Five instructions support operations on binary-coded decimal (BCD) numbers. The
arithmetic operations on packed BCD numbers are add decimal with extend (ABCD),
subtract decimal with extend (SBCD), and negate decimal with extend (NBCD). PACK and
UNPACK instructions aid in the conversion of byte encoded numeric data, such as ASCII or
EBCDIC strings, to BCD data and vice versa. Table 3–7 is a summary of the BCD
operations.
Table 3-7. BCD Operations
Instruction Operand Syntax Operand Size Operation
ABCD Dn,Dn
–(An) 8
8 source10 + destination10 + X → destination
NBCD 〈ea〉 8 0 - destination10 –X → destination
PACK –(An),–(An)
#〈data〉
Dn,Dn,# 〈data〉
16→8
16→8
unpackaged source + immediate data → packed
destination
SBCD Dn,Dn
–(An),–(An) 8
8 destination10 - source10 – X → destination
UNPK –(An)
#〈data〉
Dn,Dn,#〈data〉
8→16
8→16
packed source → unpacked source
unpacked source + immediate data →
unpacked destination
Instruction Set Summary
MOTOROLA MC68030 USER’S MANUAL 3-11
3.2.8 Program Control Instructions
A set of subroutine call and return instructions and conditional and unconditional branch
instructions perform program control operations. The no operation instruction (NOP) may be
used to force synchronization of the internal pipelines. Table 3–8 summarizes these
instructions.
Letters cc in the integer instruction mnemonics Bcc, DBcc, and Scc specify testing one of the following conditions:
CC — Carry clear GE — Greater or equal
LS — Lower or same PL — Plus
CS — Carry set GT — Greater than
LT — Less than T — Always true*
EQ — Equal HI — Higher
MI — Minus VC — Overflow clear
F — Never true* LE — -Less or equal
NE — Not equal VS — Overflow set
*Not applicable to the Bcc instructions.
Table 3-8. Program Control Operations
Instruction Operand Syntax Operand Size Operation
Integer and Floating-Point Conditional
Bcc 〈label〉 8, 16, 32 if condition true, then PC + d → PC
DBcc Dn,〈label〉 16 if condition false, then Dn — 1 → Dn
if Dn ≠ -1, then PC + d → PC
Scc 〈ea〉 8 if condition true, then 1's → destination;
else 0's → destination
Unconditional
BRA 〈label〉 8, 16, 32 PC + d → PC
BSR 〈label〉 8, 16, 32 SP — 4 → SP; PC→(SP); PC + d → PC
JMP 〈ea〉 none destination → PC
JSR 〈ea〉 none SP — 4 → SP; PC→ (SP); destination → PC
NOP none none PC + 2 → PC
Returns
RTD #〈d〉 16 (SP) → PC; SP + 4 + d → SP
RTR none none (SP) → CCR; SP + 2 → SP; (SP) → PC; SP + 4 → SP
RTS none none (SP) → PC; SP + 4→ SP
Instruction Set Summary
3-12 MC68030 USER’S MANUAL MOTOROLA
3.2.9 System Control Instructions
Privileged instructions, trapping instructions, and instructions that use or modify the
condition code register (CCR) provide system control operations. Table 3–9 summarizes
these instructions. The TRAPcc instruction uses the same conditional tests as the
corresponding program control instructions. All of these instructions cause the processor to
flush the instruction pipe.
Table 3-9. System Control Operations
Instruction Operand Syntax Operand Size Operation
Privileged
ANDI #〈data〉,SR 16 immediate data Λ SR → SR
EORI #〈data〉,SR 16 immediate data x SR → SR
MOVE 〈ea〉,SR
SR,〈ea〉 16
16 source → SR
SR → destination
MOVE USP,An
An,USP 32
32 USP → An
An → USP
MOVEC Rc,Rn
Rn,Rc 32
32 Rc → Rn
Rn → Rc
MOVES Rn, 〈ea〉
〈ea〉,Rn
8, 16, 32 Rn → destination using DFC
source using SFC → Rn
ORI #〈data〉,SR 16 immediate data V SR → SR
RESET none none assert RESET line
RTE none none (SP) → SR; SP + 2 → SP; (SP) → PC; SP + 4 → SP;
Restore stack according to format
STOP #〈data〉 16 immediate data → SR; STOP
Trap Generating
BKPT #〈data〉 none run breakpoint cycle, then trap as illegal instruction
CHK 〈ea〉,Dn 16, 32 if Dn < 0 or Dn > (ea), then CHK exception
CHK2 〈ea〉,Rn 8, 16, 32 if Rn < -lower bound or Rn > -upper bound, then CHK
exception
ILLEGAL none none SSP — 2 → SSP; Vector Offset→ (SSP);
SSP — 4 → SSP; PC→ (SSP);
SSP — 2 → SSP; SR→ (SSP);
Illegal Instruction Vector Address → PC
TRAP #〈data〉 none SSP — 2 → SSP; Format and Vector Offset→(SSP)
SSP — 4 → SSP; PC→(SSP); SSP — 2 → SSP;
SR→(SSP); Vector Address → PC
TRAPcc none
#〈data〉 none
16, 32 if cc true, then TRAP exception
TRAPV none none if V, then take overflow TRAP exception
Condition Code Register
ANDI #〈data〉,CCR 8 immediate data Λ CCR → CCR
EORI #〈data〉,CCR 8 immediate data ⊕ CCR → CCR
MOVE 〈ea〉,CCR
CCR,〈ea〉 16
16 source → CCR
CCR → destination
ORI #〈data〉,CCR 8 immediate data V CCR → CCR
Instruction Set Summary
MOTOROLA MC68030 USER’S MANUAL 3-13
3.2.10 Memory Management Unit Instructions
The PFLUSH instructions flush the address translation caches (ATCs) and can optionally
select only nonglobal entries for flushing. PTEST performs a search of the address
translation tables, storing results in the MMU status register and loading the entry into the
ATC. Table 3–10 summarizes these instructions.
3.2.11 Multiprocessor Instructions
The TAS, CAS, and CAS2 instructions coordinate the operations of processors in
multiprocessing systems. These instructions use read-modify-write bus cycles to ensure
uninterrupted updating of memory. Coprocessor instructions control the coprocessor
operations. Table 3–11 lists these instructions.
Table 3-10. MMU Instructions
Instruction Operand Syntax Operand Size Operation
PFLUSHA none none Invalidate all ATC entries
PFLUSHA.N none none Invalidate all nonglobal ATC entries
PFLUSH (An) none Invalidate ATC entries at effective address
PFLUSH.N (An) none Invalidate nonglobal ATC entries at effective address
PTEST (An) none Information about logical address → MMU status register
Table 3-11. Multiprocessor Operations (Read-Modify-Write)
Instruction Operand Syntax Operand Size Operation
Read-Modify-Write
CAS Dc,Du,〈ea〉 8, 16, 32 destination — Dc → CC; if Z then Du → destination
else destination→Dc
CAS2 Dc1:Dc2,Du1:Du2,(
Rn):(Rn) 8, 16, 32 dual operand CAS
TAS 〈ea〉 8 destination — 0; set condition codes; 1 → destination [7]
Coprocessor
cpBcc 〈label〉 16, 32 if cpcc true, then PC + d → PC
cpDBcc label,Dn 16 if cpcc false then Dn –1 → Dn
if Dn ≠ –1, then PC + d → PC
cpGEN User Defined User Defined operand → coprocessor
cpRESTORE 〈ea〉 none restore coprocessor state from 〈ea〉
cpSAVE 〈ea〉 none save coprocessor state at 〈ea〉
cpScc 〈ea〉 8 if cpcc true, then 1's → destination; else 0's → destination
cpTRAPcc none
#〈data〉
none
16, 32 if cpc true, then TRAPcc exception
Instruction Set Summary
3-14 MC68030 USER’S MANUAL MOTOROLA
3.3 INTEGER CONDITION CODES
The CCR portion of the SR contains five bits which indicate the results of many integer
instructions. Program and system control instructions use certain combinations of these bits
to control program and system flow.
The first four bits represent a condition resulting from a processor operation. The X bit is an
operand for multiprecision computations; when it is used, it is set to the value of the C bit.
The carry bit and the multiprecision extend bit are separate in the M68000 Family to simplify
programming techniques that use them (refer to Table 3–8 as an example).
The condition codes were developed to meet two criteria:
• Consistency across instructions, uses, and instances
• Meaningful Results no change unless it provides useful information
Consistency across instructions means that all instructions that are special cases of more
general instructions affect the condition codes in the same way. Consistency across
instances means that all instances of an instruction affect the condition codes in the same
way. Consistency across uses means that conditional instructions test the condition codes
similarly and provide the same results, regardless of whether the condition codes are set by
a compare, test, or move instruction.
In the instruction set definitions, the CCR is shown as follows:
where:
X (extend)
Set to the value of the C bit for arithmetic operations. Otherwise not affected or set to
a specified result.
N (negative)
Set if the most significant bit of the result is set. Cleared otherwise.
Z (zero)
Set if the result equals zero. Cleared otherwise.
V (overflow)
Set if arithmetic overflow occurs. This implies that the result cannot be represented in
the operand size. Cleared otherwise.
C (carry)
Set if a carry out of the most significant bit of the operand occurs for an addition. Also
set if a borrow occurs in a subtraction. Cleared otherwise.
XNZVC
Instruction Set Summary
MOTOROLA MC68030 USER’S MANUAL 3-15
3.3.1 Condition Code Computation
Most operations take a source operand and a destination operand, compute, and store the
result in the destination location. Single-operand operations take a destination operand,
compute, and store the result in the destination location. Table 3–12 lists each instruction
and how it affects the condition code bits.
Table 3-12. Condition Code Computations (Sheet 1 of 2)
Operations X N Z V C Special Definition
ABCD * U ? U ? C =-Decimal Carry
Z =-Z Λ Rm Λ . . . Λ R0
ADD, ADDI, ADDQ * * * ? ? V = Sm Λ Dm Λ Rm V Sm Λ Dm Λ Rm
C = Sm Λ Dm V Rm Λ Dm V Sm Λ Rm
ADDX * * ? ? ? V = Sm Λ Dm Λ Rm V Sm Λ Dm Λ Rm
C = Sm Λ Dm V Rm Λ Dm V Sm Λ Rm
Z = Z Λ Rm Λ . . . Λ R0
AND, ANDI, EOR, EORI,
MOVEQ, MOVE, OR, ORI
CLR, EXT, NOT, TAS, TST
— * * 0 0
CHK — * U U U
CHK2, CMP2 — U ? U ? Z = (R = LB) V (R = UB)
C = (LB < = UB) Λ (IR < LB) V (R > UB))
V = (UB <LB) Λ (R >UB) Λ (R <LB)
SUB, SUBI, SUBQ * * * ? ? V = Sm Λ Dm Λ Rm V Sm Λ Dm Λ Rm
C = Sm Λ Dm V Rm Λ Dm V Sm Λ Rm
SUBX * * ? ? ? V = Sm Λ Dm Λ Rm V Sm Λ Dm Λ Rm
C = Sm Λ Dm V Rm Λ Dm V Sm Λ Rm
Z = Z Λ Rm Λ . . . Λ R0
CAS, CAS2, CMP, CMPI,
CMPM — * * ? ? V = Sm Λ Dm Λ Rm V Sm Λ Dm Λ Rm
C = Sm Λ Dm V Rm Λ Dm V Sm Λ Rm
DIVS, DUVI — * * ? 0 V = Division Overflow
MULS, MULU — * * ? 0 V = Multiplication Overflow
SBCD, NBCD * U U ? C = Decimal Borrow
Z = Z Λ Rm Λ . . . Λ R0
NEG * * * ? ? V = Dm Λ Rm
C = Dm V Rm
NEGX * * ? ? ? V = Dm Λ Rm
C = Dm V Rm
Z = Z Λ Rm Λ . . . Λ R0
Instruction Set Summary
3-16 MC68030 USER’S MANUAL MOTOROLA
— = Not Affected Rm = Result Operand — Most Significant Bit
U = Undefined, Result Meaningless R = Register Tested
? = Other — See Special Definition n = Bit Number
* = General Case r = Shift Count
X = C LB = Lower Bound
N = Rm UB = Upper Bound
Z = Rm Λ . . . Λ R0 Λ= Boolean AND
Sm = Destination Operand — Most Significant Bit V = Boolean OR
Dm = Destination Operand — Most Significant Bit Rm = NOT Rm
Table 3-12. Condition Code Computations (Continued)
Operations X N Z V C Special Definition
BTST, BCHG, BSET, BCLR — — ? — — Z = Dn
BFTST, BFCHG, BFSET,
BFCLR — ? ? 0 0 N = Dm
Z = Dm Λ DM –1 Λ . . . Λ D0
BFEXTS, BFEXTU, BFFFO — ? ? 0 0 N = Sm
Z = Sm Λ Sm –1 Λ . . . Λ S0
BFINS — ? ? 0 0 N = Dm
Z = Dm Λ DM–1 Λ . . . Λ D0
ASL * * * V = Dm Λ (Dm –1 V . . . V Dm –r) V Dm Λ
(Dm –1 V . . . + Dm –r)
C = Dm –r + 1
ASL (R = 0) * * 0 0
LSL, ROXL * * * 0 ? C = Dm –r + 1
LSR (r = 0) — * * 0 0
ROXL (r = 0) — * * 0 ? C = X
ROL — * * 0 ? C = Dm –r + 1
ROL (r = 0) — * * 0 0
ASR, LSR, ROXR * * * 0 ? C = Dr –1
ASR, LSR (r = 0) — * * 0 0
ROXR (r = 0) — * * 0 ? C = X
ROR — * * 0 ? C = Dr –1
ROR (r = 0) — * * 0 0
Instruction Set Summary
MOTOROLA MC68030 USER’S MANUAL 3-17
3.3.2 Conditional Tests
Table 3–13 lists the condition names, encodings, and tests for the conditional branch and
set instructions. The test associated with each condition is a logical formula using the current
states of the condition codes. If this formula evaluates to one, the condition is true. If the
formula evaluates to zero, the condition is false. For example, the T condition is always true,
and the EQ condition is true only if the Z bit condition code is currently true.
• = Boolean AND
+ = Boolean OR
N = Boolean NOT N
*Not available for the Bcc instruction.
Table 3-13. Conditional Tests
Mnemonic Condition Encoding Test
T* True 0000 1
F* False 0001 0
HI High 0010 C •Z
LS Low or Same 0011 C + Z
CC(HS) Carry Clear 0100 C
CS(LO) Carry Set 0101 C
NE Not Equal 0110 Z
EQ Equal 0111 Z
VC Overflow Clear 1000 V
VS Overflow Set 1001 V
PL Plus 1010 N
MI Minus 1011 N
GE Greater or Equal 1100 N •V + N •V
LT Less Than 1101 N •V + N •V
GT Greater Than 1110 N •V •Z + N • V •Z
LE Less or Equal 1111 Z + N •V + N • V
Instruction Set Summary
3-18 MC68030 USER’S MANUAL MOTOROLA
3.4 INSTRUCTION SET SUMMARY
Table 3–14 provides a alphabetized listing of the MC68030 instruction set listed by opcode,
operation, and syntax.
Table 3–14 use notational conventions for the operands, the subfields and qualifiers, and
the operations performed by the instructions. In the syntax descriptions, the left operand is
the source operand, and the right operand is the destination operand. The following list
contains the notations used in Table 3–14.
Notation for operands:
PC — Program counter
SR — Status register
V — Overflow condition code
Immediate Data — Immediate data from the instruction
Source — Source contents
Destination — Destination contents
Vector — Location of exception vector
+ inf — Positive infinity
–inf — Negative infinity
〈fmt〉— Operand data format: byte (B) word (W), long
(L), single (S), double (D), extended (X), or
packed (P)
FPm — One of eight floating-point data registers (always
specifies the source register)
FPn — One of eight floating-point data registers (always
specifies the destination register)
Notation for subfields and qualifiers:
〈bit〉 of (operand〉 — Selects a single bit of the operand
〈ea〉 {offset:width} — Selects a bit field
(〈operand〉) — The contents of the referenced location
〈operand〉 10 — The operand is binary-coded decimal; operations are per-
formed in decimal
(〈address register〉) — The register indirect operation
–(〈address register〉) — Indicates that the operand register points to the memory
(〈address register〉) + — Location of the instruction operand — the optional mode
qualifiers are -, +, (d), and (d,ix)
#xxx or #〈data〉— Immediate data that follows the instruction word(s)
Instruction Set Summary
MOTOROLA MC68030 USER’S MANUAL 3-19
Notations for operations that have two operands, written 〈operand〉 〈op〉 〈operand〉 , where
〈op〉 is one of the following:
→— The source operand is moved to the destination operand
↔— The two operands are exchanged
+ — The operands are added
– — The destination operand is subtracted from the source
operand
x — The operands are multiplied
÷— The source operand is divided by the destination operand
< — Relational test, true if source operand is less than destina-
tion operand
> — Relational test, true if source operand is greater than des-
tination operand
V — Logical OR
⊕— Logical exclusive OR
Λ— Logical AND
shifted by, rotated by — The source operand is shifted or rotated by the number of
positions specified by the second operand
Notation for single-operand operations:
~〈operand〉 — The operand is logically complemented
〈operand〉 sign-extended— The operand is sign extended; all bits of the upper portion
are made equal to the high-order bit of the lower portion
〈operand〉 tested — The operand is compared to zero and the condition codes
are set appropriately
Notation for other operations:
TRAP — Equivalent to Format/Offset Word→ (SSP); SSP –2
→ SSP; PC→ (SSP); SSP – 4 → SSP; SR→ (SSP);
SSP–2 → SSP; (vector) → PC
STOP — Enter the stopped state, waiting for the interrupts
If 〈condition〉 then — The condition is tested. If true, the operations
〈operations〉 else — after "then'' are performed. If the condition is
〈operations〉— false and the optional "else'' clause is present, the opera-
tions after "else" are performed. If the condition is false and
else is omitted, the instruction performs no operation. Refer
to the Bcc instruction description as an example.
Instruction Set Summary
3-20 MC68030 USER’S MANUAL MOTOROLA
Table 3-14. Instruction Set Summary (Sheet 1 of 5)
Opcode Operation Syntax
ABCD Source10 + Destination10 + X → Destination ABCD Dy,Dx
ABCD –(Ay),–(Ax)
ADD Source + Destination → -Destination ADD 〈ea〉,Dn
ADD Dn,〈ea〉
ADDA Source + Destination → Destination ADDA 〈ea〉,An
ADDI Immediate Data + Destination → Destination ADDI #〈data〉,〈ea〉
ADDQ Immediate Data + Destination → Destination ADDQ #〈data〉,〈ea〉
ADDX Source + Destination + X → Destination ADDX Dy,Dx
ADDX –(Ay),–(Ax)
AND Source Λ Destination → Destination AND 〈ea〉,Dn
AND Dn,〈ea〉
ANDI Immediate Data Λ Destination → Destination ANDI #〈data〉,〈ea〉
ANDI
to CCR Source Λ CCR → CCR ANDI #〈data〉,CCR
ANDI
to SR If supervisor state
then Source Λ SR → SR
else TRAP
ANDI #〈data〉,SR
ASL,ASR Destination Shifted by 〈count〉 → Destination ASd Dx,Dy
ASd #〈data〉,Dy
ASd 〈ea〉
Bcc If (condition true) then PC + d → PC Bcc (label〉
BCHG ∼ (〈number〉 of Destination) → Z;
∼ (〈number〉 of Destination) → 〈bit number〉 of Destination BCHG Dn,〈ea〉BCHG #〈data〉,〈ea〉
BCLR ∼ (〈bit number〉 of Destination) → Z;
0 → 〈bit number〉 of Destination BCLR Dn,〈ea〉BCLR #〈data〉,〈ea〉
BFCHG ∼ (〈bit field〉 of Destination) → 〈bit field〉 of Destination BFCHG 〈ea〉{offset:width}
BFCLR 0 → 〈bit field〉 of Destination BFCLR 〈ea〉{offset:width}
BFEXTS 〈bit field〉 of Source → Dn BFEXTS 〈ea〉{offset:width},Dn
BFEXTU (bit offset〉 of Source → Dn BFEXTU 〈ea〉{offset:width},Dn
BFFFO (bit offset〉 of Source Bit Scan → Dn BFFFO 〈ea〉{offset:width},Dn
BFINS Dn → 〈bit field〉 of Destination BFINS Dn,〈ea〉{offset:width}
BFSET 1s → 〈bit field〉 of Destination BFSET 〈ea〉{offset:width}
BFTST 〈bit field〉 of Destination BFTST 〈ea〉{offset:width}
BKPT Run breakpoint acknowledge cycle;
TRAP as illegal instruction BKPT # 〈data〉
BRA PC + d → PC BRA (label〉
BSET ~ (〈bit number〉 of Destination) → Z;
1 → 〈bit number〉 of Destination BSET Dn,〈ea〉BSET #〈data〉,〈ea〉
BSR SP – 4 → SP; PC → (SP); PC + d → PC BSR (label〉
BTST –(〈bit number〉 of Destination) → Z; BTST Dn,〈ea〉BTST #〈data〉,〈ea〉
Instruction Set Summary
MOTOROLA MC68030 USER’S MANUAL 3-21
Table 3-14. Instruction Set Summary (Sheet 2 of 5)
Opcode Operation Syntax
CAS
CAS2 CAS Destination Compare Operand → cc;
if Z, Update Operand → Destination
else Destination → Compare Operand
CAS2 Destination 1 Compare 1 → cc;
if Z, Destination 2 Compare → cc;
if Z, Update 1 → Destination 1; Update 2 → Destination 2
else Destination 1 → Compare 1; Destination 2 →Compare 2
CAS Dc,Du,〈ea〉CAS2
Dc1:Dc2,Du1:Du2,(Rn1):(Rn2)
CHK If Dn < 0 or >-Source then TRAP CHK 〈ea〉,Dn
CHK2 If Rn < lower bound or
Rn > upper bound
then TRAP
CHK2 〈ea〉,Rn
CLR 0 → Destination CLR 〈ea〉
CMP Destination — Source → cc CMP 〈ea〉,Dn
CMPA Destination — Source CMPA 〈ea〉,An
CMPI Destination — Immediate Data CMPI #〈data〉,〈ea〉
CMPM Destination — Source → cc CMPM (Ay) +,(Ax) +
CMP2 Compare Rn < lower-bound or
Rn > upper-bound
and Set Condition Codes
CMP2 〈ea〉,Rn
cpBcc If cpcc true then scanPC + d → PC cpBcc (label〉
cpDBcc If cpcc false then (Dn –1 → Dn;
if Dn ≠ –1 then scanPC + d → PC cpDBcc Dn,(label〉
cpGEN Pass Command Word to Coprocessor cpGEN (parameters as defined by
coprocessorL
cpRESTORE If supervisor state
then Restore Internal State of Coprocessor
else TRAP
cpRESTORE 〈ea〉
cpSAVE If supervisor state
the Save Internal State of Coprocessor
else TRAP
cpSAVE 〈save〉
cpScc If cpcc true then 1s → Destination
else 0s → Destination
cpTRAPcc If cpcc true then TRAP cpTRAPcc
cpTRAPcc #〈data〉
DBcc If condition false then (Dn–1 → Dn;
If Dn ≠ –1 then PC + d → PC) DBcc Dn,(label〉
DIVS
DIVSL Destination/Source → Destination DIVS.W 〈ea〉,Dn32/16 → 16r:16q
DIVS.L 〈ea〉,Dq 32/32 → 32q
DIVS.L 〈ea〉,Dr:Dq 64/32 → 32r:32q
DIVSL.L 〈ea〉,Dr:Dq32/32 → 32r:32q
DIVU
DIVUL Destination/Source → Destination DIVU.W 〈ea〉,Dn32/16 → 16r:16q
DIVU.L 〈ea〉,Dq 32/32 → 32q
DIVU.L 〈ea〉,Dr:Dq 64/32 → 32r:32q
DIVUL.L 〈ea〉,Dr:Dq32/32 → 32r:32q
EOR Source ⊕ Destination → Destination EOR Dn,〈ea〉
EORI Immediate Data ⊕ Destination → Destination EORI #〈data〉,〈ea〉
Instruction Set Summary
3-22 MC68030 USER’S MANUAL MOTOROLA
Table 3-14. Instruction Set Summary (Sheet 3 of 5)
Opcode Operation Syntax
EORI
to CCR Source ⊕ CCR → CCR EORI #〈data〉,CCR
EORI
to SR If supervisor state
then Source ⊕ SR → SR
else TRAP
EORI #〈data〉,SR
EXG Rx ↔ Ry EXG Dx,Dy
EXG Ax,Ay
EXG Dx,Ay
EXG Ay,Dx
EXT
EXTB Destination Sign-Extended → Destination EXT.W Dn extend byte to word
EXT.L L Dn extend word to long word
EXTB.L Dn extend byte to long word
ILLEGAL SSP–2 → SSP; Vector Offset → (SSP);
SSP–4 → SSP; PC → (SSP);
SSP–2 → SSP; SR → (SSP);
Illegal Instruction Vector Address → PC
ILLEGAL
JMP Destination Address → PC JMP 〈ea〉
JSR SP–4 → SP; PC → (SP)
Destination Address → PC JSR 〈ea〉
LEA 〈ea〉 → An LEA 〈ea〉,An
LINK SP — 4 → SP; An → (SP)
SP → An, SP + d → SP LINK An, #(displacement〉
LSL,LSR Destination Shifted by 〈count〉 → Destination LSd5 Dx,Dy
LSd5 #〈data〉,Dy
LSd5 〈ea〉
MOVE Source → Destination MOVE 〈ea〉,〈ea〉
MOVEA Source → Destination MOVEA 〈ea〉,An
MOVE
from CCR CCR → Destination MOVE CCR,〈ea〉
MOVE
to CCR Source → CCR MOVE 〈ea〉,CCR
MOVE
from SR If supervisor state
then SR → Destination
else TRAP
MOVE SR,〈ea〉
MOVE
to SR If supervisor state
then Source → SR
else TRAP
MOVE 〈ea〉,SR
MOVE
USP If supervisor state
then USP → An or An → USP
else TRAP
MOVE USP,An
MOVE An,USP
MOVEC If supervisor state
then Rc → Rn or Rn → Rc
else TRAP
MOVEC Rc,Rn
MOVEC Rn,Rc
MOVEM Registers → Destination
Source → Registers MOVEM register list,〈ea〉MOVEM
〈ea〉,register list
MOVEP Source → Destination MOVEP Dx,(d,Ay)
MOVEP (d,Ay),Dx
MOVEQ Immediate Data → Destination MOVEQ #〈data〉,Dn
Instruction Set Summary
MOTOROLA MC68030 USER’S MANUAL 3-23
Table 3-14. Instruction Set Summary (Sheet 4 of 5)
Opcode Operation Syntax
MOVES If supervisor state
then Rn → Destination [DFC] or Source [SFC] → Rn
else TRAP
MOVES Rn,〈ea〉MOVES 〈ea〉,Rn
MULS Source y-Destination → Destination MULS.W 〈ea〉,Dn 16 x 16 → 32
MULS.L 〈ea〉,Dl 32 x 32 → 32
MULS.L 〈ea〉,Dh:Dl 32 x 32 → 64
MULU Source y-Destination → Destination MULU.W 〈ea〉,Dn 16 x 16 → 32
MULU.L 〈ea〉,Dl 32 x 32 → 32
MULU.L 〈ea〉,Dh:Dl 32 x 32 → 64
NBCD 0 — (Destination10) — X → Destination NBCD 〈ea〉
NEG 0 — (Destination) → Destination NEG 〈ea〉
NEGX 0 — (Destination) — X → Destination NEGX 〈ea〉
NOP None NOP
NOT ∼ Destination → Destination NOT 〈ea〉
OR Source V Destination → Destination OR 〈ea〉,Dn
OR Dn,〈ea〉
ORI Immediate Data V Destination → Destination ORI #〈data〉,〈ea〉
ORI
to CCR Source V CCR → CCR ORI #〈data〉,CCR
ORI
to SR If supervisor state
then Source V SR → SR
else TRAP
ORI #〈data〉,SR
PACK Source (Unpacked BCD) + adjustment → Destintion
(Packed BCD) PACK –(Ax),–(Ay),#(adjustment〉
PACK Dx,Dy,#(adjustment〉
PEA Sp –4 → SP; 〈ea〉 → (SP) PEA 〈ea〉
PFLUSH If supervisor state
then invalidate instruction and data ATC entries for
destination address
else TRAP
PLOAD If supervisor state
then entry → ATC
else TRAP
PMOVE If supervisor state
then (Source) → MRn or MRn → (Destination)
PTEST If supervisor state
then logical address status → MMUSR; entry → ATC
else TRAP
RESET If supervisor state
then Assert RSTO Line
else TRAP
RESET
ROL,ROR Destination Rotated by 〈count〉 → Destination ROd5 Rx,Dy
ROd5 #〈data〉,Dy
ROd5 〈ea〉
ROXL,
ROXR Destination Rotated with X by 〈count〉 → Destination ROXd5 Dx,Dy
ROXd5 #〈data〉,Dy
ROXd5 〈ea〉
Instruction Set Summary
3-24 MC68030 USER’S MANUAL MOTOROLA
NOTES:
1. Specifies either the instruction (IC), data (DC), or IC/DC caches.
2. Where r is rounding precision, S or D.
3. A list of any combination of the eight floating-point data registers, with individual register names separated by a
slash (/) and/or contiguous bloc ks of registers specified by the first and last register names separated b y a dash
( –).
4. A list of any combination of the three floating-point system control registers (FPCR, FPSR, and FPIAR) with
indvidual register names separated by a slash (/).
5. Where d is direction, L or R.
Table 3-14. Instruction Set Summary (Concluded)
Opcode Operation Syntax
RTD (SP) → PC; SP + 4 + d → SP RTD #〈displacement〉
RTE If-supervisor-state
then (SP) → SR; SP+2 → SP; (SP) → PC;
SP + 4 → SP;
restore state and deallocate stack according to (SP)
else TRAP
RTE
RTM Reload Saved Module State from Stack RTM Rn
RTR (SP) → CCR; SP + 2 → SP;
(SP) → PC; SP + 4 → SP RTR
RTS (SP) → PC; SP + 4 → SP RTS
SBCD Destination10 --Source10 –X → Destination SBCD Dx,Dy
SBCD –(Ax),–(Ay)
Scc If condition true
then 1s → Destination
else 0s → Destination
Scc 〈ea〉
STOP If supervisor state
then Immediate Data → SR; STOP
else TRAP
STOP #〈data〉
SUB Destination — Source → Destination SUB 〈ea〉,Dn
SUB Dn,〈ea〉
SUBA Destination — Source → Destination SUBA 〈ea〉,An
SUBI Destination — Immediate Data → Destination SUBI #〈data〉,〈ea〉
SUBQ Destination — Immediate Data → Destination SUBQ #〈data〉,〈ea〉
SUBX Destination — Source – X → Destination SUBX Dx,Dy
SUBX –(Ax),–(Ay)
SWAP Register [31:16] ↔ Register [15:0] SWAP Dn
TAS Destination Tested → Condition Codes; 1 → bit 7 of Destination TAS 〈ea〉
TRAP SSP –2 → SSP; Format/Offset → (SSP);
SSP – 4 → SSP; PC → (SSP); SSP – 2 → SSP;
SR → (SSP); Vector Address → PC
TRAP # (vector〉
TRAPcc If cc then TRAP TRAPcc
TRAPcc.W # 〈data〉TRAPcc.L # 〈data〉
TRAPV If V then TRAP TRAPV
TST Destination Tested → Condition Codes TST 〈ea〉
UNLK An → SP; (SP) → An; SP + 4 → SP UNLK An
UNPK Source (Packed BCD) + adjustment → Destination (Unpacked BCD) UNPACK –(Ax),–(Ay),#(adjustment〉
UNPACK Dx,Dy,#(adjustment〉
Instruction Set Summary
MOTOROLA MC68030 USER’S MANUAL 3-25
3.5 INSTRUCTION EXAMPLES
The following paragraphs provide examples of how to use selected instructions.
3.5.1 Using the CAS and CAS2 Instructions
The CAS instruction compares the value in a memory location with the value in a data
register, and copies a second data register into the memory location if the compared values
are equal. This provides a means of updating system counters, history information, and
globally shared pointers. The instruction uses an indivisible read-modify-write cycle; after
CAS reads the memory location, no other instruction can change that location before CAS
has written the new value. This provides security in single-processor systems, in
multitasking environments, and in multiprocessor environments. In a single-processor
system, the operation is protected from instructions of an interrupt routine. In a multitasking
environment, no other task can interfere with writing the new value of a system variable. In
a multiprocessor environment, the other processors must wait until the CAS instruction
completes before accessing a global pointer.
The following code fragment shows a routine to maintain a count, in location SYS_CNTR,
of the executions of an operation that may be performed by any process or processor in a
system. The routine obtains the current value of the count in register D0 and stores the new
count value in register D1. The CAS instruction copies the new count into SYS_CNTR if it
is valid. However, if another user has incremented the counter between the time the count
was stored and the read-modify-write cycle of the CAS instruction, the write portion of the
cycle copies the new count in SYS_CNTR into D0, and the routine branches to repeat the
test. The following code sequence guarantees that SYS_CNTR is correctly incremented.
MOVE.W SYS_CNTR,D0 get the old value of the counter
INC_LOOP MOVE.W D0,D1 make a copy of it
ADDQ.W #1,D1 and increment it
CAS.W D0,D1,SYS_CNTR if countr value is still the same, update it
BNE INC_LOOP if not, try again
Instruction Set Summary
3-26 MC68030 USER’S MANUAL MOTOROLA
The CAS and CAS2 instructions together allow safe operations in the manipulation of
system linked lists. Controlling a single location, HEAD in the example, manages a last-in-
first-out linked list (see Figure 3–2). If the list is empty, HEAD contains the NULL pointer (0);
otherwise, HEAD contains the address of the element most recently added to the list. The
code fragment shown in Figure 3–2 illustrates the code for inserting an element. The MOVE
instructions load the address in location HEAD into D0 and into the NEXT pointer in the
element being inserted, and the address of the new element into D1. The CAS instruction
stores the address of the inserted element into location HEAD if the address in HEAD
remains unaltered. If HEAD contains a new address, the instruction loads the new address
into D0 and branches to the second MOVE instruction to try again.
The CAS2 instruction is similar to the CAS instruction except that it performs two
comparisons and updates two variables when the results of the comparisons are equal. If
the results of both comparisons are equal, CAS2 copies new values into the destination
addresses. If the result of either comparison is not equal, the instruction copies the values
in the destination addresses into the compare operands.
Figure 3-2. Linked List Insertion
SINSERT MOVE.L HEAD.D0
MOVE.L D0, (NEXT, A1)
MOVE.L A1, D1
CAS.L D0, D1, HEAD
BNE SILOOP
ALLOCATE NEW ENTRY, ADDRESS IN A1
MOVE HEAD POINTER VALUE TO D0
ESTABLISH FORWARD LINK IN NEW ENTRY
MOVE NEW ENTRY POINTER VALUE TO D1
IF WE STILL POINT TO TOP OF STACK, UPDATE THE HEAD POINTER
IF NOT, TRY AGAIN
SILOOP
ENTRY
+ NEXT
ENTRY
+ NEXT
ENTRY
+ NEXT
ENTRY
+ NEXT
NEW
HEAD
NEW HEAD
AFTER INSERTING AN ELEMENT:
BEFORE INSERTING AN ELEMENT:
ENTRY
+ NEXT
ENTRY
+ NEXT
?
Instruction Set Summary
MOTOROLA MC68030 USER’S MANUAL 3-27
The next code (see Figure 3–3) fragment shows the use of a CAS2 instruction to delete an
element from a linked list. The first LEA instruction loads the effective address of HEAD into
A0. The MOVE instruction loads the address in pointer HEAD into D0. The TST instruction
checks for an empty list, and the BEQ instruction branches to a routine at label SDEMPTY
if the list is empty. Otherwise, a second LEA instruction loads the address of the NEXT
pointer in the newest element on the list into A1, and the following MOVE instruction loads
the pointer contents into D1. The CAS2 instruction compares the address of the newest
structure to the value in HEAD and the address in D1 to the pointer in the address in A1. If
no element has been inserted or deleted by another routine while this routine has been
executing, the results of these comparisons are equal, and the CAS2 instruction stores the
new value into location HEAD. If an element has been inserted or deleted, the CAS2
instruction loads the new address in location HEAD into D0, and the BNE instruction
branches to the TST instruction to try again.
Figure 3-3. Linked List Deletion
HEAD
AFTER DELETING AN ELEMENT:
BEFORE DELETING AN ELEMENT:
SDELETE
SDLOOP
SDEMPTY
LEA HEAD, A0
MOVE.L (A0), D0
TST.L D0
BEQ SDEMPTY
LEA (NEXT, D0), A1
MOVE.L (A1), D1
CAS2.L D0:D1, D1:D1, (A0):(A1)
BNE SDLOOP
LOAD ADDRESS OF HEAD POINTER INTO A0
MOVE VALUE OF HEAD POINTER INTO D0
CHECK FOR NULL HEAD POINTER
IF EMPTY, NOTHING TO DELETE
LOAD ADDRESS OF FORWARD LINK INTO A1
PUT FORWARD LINK VALUE IN D1
IF STILL POINT TO ENTRY TO BE DELETED, THEN UPDATE HEAD
AND FORWARD POINTERS
IF NOT, TRY AGAIN
SUCCESSFUL DELETION, ADDRESS OF DELETED ENTRY IN D0
(MAY BE NULL)
ENTRY
+ NEXT
ENTRY
+ NEXT
ENTRY
+ NEXT
ENTRY
+ NEXT
HEAD
ENTRY
+ NEXT
ENTRY
+ NEXT
Instruction Set Summary
3-28 MC68030 USER’S MANUAL MOTOROLA
The CAS2 instruction can also be used to correctly maintain a first-in-first-out doubly linked
list. A doubly linked list needs two controlled locations, LIST_PUT and LIST_GET, which
contain pointers to the last element inserted in the list and the next to be removed,
respectively. If the list is empty, both pointers are NULL (0).
The code fragment shown in Figure 3–4 illustrates the insertion of an element in a doubly
linked list. The first two instructions load the effective addresses of LIST_PUT and
LIST_GET into registers A0 and A1, respectively. The next instruction moves the address
of the new element into register D2. Another MOVE instruction moves the address in
LIST_PUT into register D0. At label DILOOP, a TST instruction tests the value in D0, and
the BEQ instruction branches to the MOVE instruction when D0 is equal to zero. Assuming
the list is empty, this MOVE instruction is executed next; it moves the zero in D0 into the
NEXT and LAST pointers of the new element. Then the CAS2 instruction moves the address
of the new element into both LIST_PUT and LIST_GET, assuming that both of these
pointers still contain zero. If not, the BNE instruction branches to the TST instruction at label
DILOOP to try again. This time, the BEQ instruction does not branch, and the following
MOVE instruction moves the address in D0 to the NEXT pointer of the new element. The
CLR instruction clears register D1 to zero, and the MOVE instruction moves the zero into
the LAST pointer of the new element. The LEA instruction loads the address of the LAST
pointer of the most recently inserted element into register A1. Assuming the LIST_PUT
pointer and the pointer in A1 have not been changed, the CAS2 instruction stores the
address of the new element into these pointers.
The code fragment to delete an element from a doubly linked list is similar (see Figure 3–5).
The first two instructions load the effective addresses of pointers LIST_PUT and LIST_GET
into registers A0 and A1, respectively. The MOVE instruction at label DDLOOP moves the
LIST_GET pointer into register D1. The BEQ instruction that follows branches out of the
routine when the pointer is zero. The MOVE instruction moves the LAST pointer of the
element to be deleted into register D2. Assuming this is not the last element in the list, the
Z condition code is not set, and the branch to label DDEMPTY does not occur. The LEA
instruction loads the address of the NEXT pointer of the element at the address in D2 into
register A2. The next instruction, a CLR instruction, clears register D0 to zero. The CAS2
instruction compares the address in D1 to the LIST-GET pointer and to the address in
register A2. If the pointers have not been updated, the CAS2 instruction loads the address
in D2 into the LIST_GET pointer and zero into the address in register A2.
Instruction Set Summary
MOTOROLA MC68030 USER’S MANUAL 3-29
When the list contains only one element, the routine branches to the CAS2 instruction at
label DDEMPTY after moving a zero pointer value into D2. This instruction checks the
addresses in LIST_PUT and LIST_GET to verify that no other routine has inserted another
element or deleted the last element. Then the instruction moves zero into both pointers, and
the list is empty.
Figure 3-4. Doubly Linked List Insertion
BEFORE INSERTING NEW ENTRY:
DINSERT
DILOOP
DIEMPTY
DIDONE
LEA LIST_PUT, A0
LEA LIST_GET, A1
MOVE.L A2, D2
MOVE.L (A0), D0
TST.L D0
BEQ DIEMPTY
MOVE.L D0, (NEXT, A2)
CLR.L D1
MOVE.L D1, (LAST, A2)
LEA (LAST, D0), A1
CAS2.L D0:D1,D2:D2,(A0):(A1)
BNE DILOOP
BRA DIDONE
MOVE.L D0, (NEXT, A2)
MOVE.L D0, (LAST, A2)
CAS2.L D0:D0,D2:D2,(A0):(A1)
BNE DILOOP
(ALLOCATE NEW LIST ENTRY, LOAD ADDRESS INTO A2)
LOAD ADDRESS OF HEAD POINTER INTO A0
LOAD ADDRESS OF TAIL POINTER INTO A1
LOAD NEW ENTRY POINTER INTO D2
LOAD POINTER TO HEAD ENTRY INTO D0
IS HEAD POINTER NULL, (0 ENTRIES IN LIST)?
IF SO, WE NEED ONLY TO ESTABLISH POINTERS
PUT HEAD POINTER INTO FORWARD POINTER OF NEW ENTRY
PUT NULL POINTER VALUE INTO D1
PUT NULL POINTER IN BACKWARD POINTER OF NEW ENTRY
LOAD BACKWARD POINTER OF OLD HEAD ENTRY INTO A1
IF WE STILL POINT TO OLD HEAD ENTRY, UPDATE POINTERS
IF NOT, TRY AGAIN
PUT NULL POINTER IN FORWARD POINTER OF NEW ENTRY
PUT NULL POINTER IN BACKWARD POINTER OF NEW ENTRY
IF WE STILL HAVE NO ENTRIES, SET BOTH POINTERS TO THIS ENTRY
IF NOT, TRY AGAIN
SUCCESSFUL LIST ENTRY INSERTION
ENTRY ENTRY ENTRY
+ NEXT + NEXT + NEXT
AFTER INSERTING NEW ENTRY:
+ LAST+ LAST+ LAST
NEW ENTRY LIST_PUT LIST_GET
LIST_PUT
ENTRY ENTRY
+ NEXT + NEXT+ LAST+ LAST
LIST_GET
ENTRY
+ NEXT+ LAST
Instruction Set Summary
3-30 MC68030 USER’S MANUAL MOTOROLA
3.5.2 Nested Subroutine Calls
The LINK instruction pushes an address onto the stack, saves the stack address at which
the address is stored, and reserves an area of the stack. Using this instruction in a series of
subroutine calls results in a linked list of stack frames.
The UNLK instruction removes a stack frame from the end of the list by loading an address
into the stack pointer and pulling the value at that address from the stack. When the operand
of the instruction is the address of the link address at the bottom of a stack frame, the effect
is to remove the stack frame from the stack and from the linked list.
Figure 3-5. Doubly Linked List Deletion
AFTER DELETING ENTRY:
BEFORE DELETING ENTRY:
DDELETE
DDLOOP
DDEMPTY
DDDONE
LEA LIST_PUT, A0
LEA LIST_GET, A1
MOVE.L (A1),D1
BEQ DDDONE
MOVE.L (LAST,D1),D2
BEQ DDEMPTY
LEA (NEXT,D2),A2
CLR.L D0
CAS2.L D1:D1,D2:D0,(A1):(A2)
BNE DDLOOP
BRA DDDONE
CAS2.L D1:D1,D2:D2,(A1):(A0)
BNE DDLOOP
GET ADDRESS OF HEAD POINTER IN A0
GET ADDRESS OF TAIL POINTER IN A1
MOVE TAIL POINTER INTO D1
IF NO LIST, QUIT
PUT BACKWARD POINTER IN D2
IF ONLY ONE ELEMENT, UPDATE POINTERS
PUT ADDRESS OF FORWARD POINTER IN A2
PUT NULL POINTER VALUE IN D0
IF BOTH POINTERS STILL POINT TO THIS ENTRY , UPDATE THEM
IF NOT, TRY AGAIN
IF STILL FIRST ENTRY, SET HEAD AND TAIL POINTERS TO NULL
IF NOT, TRY AGAIN
SUCCESSFUL ENTRY DELETION, ADDRESS OF DELETED ENTRY IN D1
(MAY BE NULL)
ENTRY ENTRY ENTRY
+ NEXT + NEXT + NEXT+ LAST+ LAST+ LAST
LIST_PUT LIST_GET
LIST_PUT
ENTRY ENTRY
+ NEXT + NEXT+ LAST+ LAST
DELETED ENTRY
LIST_GET
ENTRY
+ NEXT+ LAST
Instruction Set Summary
MOTOROLA MC68030 USER’S MANUAL 3-31
3.5.3 Bit Field Operations
One data type provided by the MC68030 is the bit field, consisting of as many as 32
consecutive bits. A bit field is defined by an offset from an effective address and a width
value. The offset is a value in the range of 231 through 231 1 from the most significant bit
(bit 7) at the effective address. The width is a positive number, 1–32. The most significant
bit of a bit field is bit 0; the bits number in a direction opposite to the bits of an integer.
The instruction set includes eight instructions that have bit field operands. The insert bit field
(BFINS) instruction inserts a bit field stored in a register into a bit field. The extract bit field
signed (BFEXTS) instruction loads a bit field into the least significant bits of a register and
extends the sign to the left, filling the register. The extract bit field unsigned (BFEXTU) also
loads a bit field, but zero fills the unused portion of the destination register.
The set bit field (BFSET) instruction sets all the bits of a field to ones. The clear bit field
(BFCLR) instruction clears a field. The change bit field (BFCHG) instruction complements
all the bits in a bit field. These three instructions all test the previous value of the bit field,
setting the condition codes accordingly. The test bit field (BFTST) instruction tests the value
in the field, setting the condition codes appropriately without altering the bit field. The find
first one in bit field (BFFFO) instruction scans a bit field from bit 0 to the right until it finds a
bit set to one and loads the bit offset of the first set bit into the specified data register. If no
bits in the field are set, the field offset and the field width is loaded into the register.
An important application of bit field instructions is the manipulation of the exponent field in a
floating-point number. In the IEEE standard format, the most significant bit is the sign bit of
the mantissa. The exponent value begins at the next most significant bit position; the
exponent field does not begin on a byte boundary. The extract bit field (BFEXTU) instruction
and the BFTST instruction are the most useful for this application, but other bit field
instructions can also be used.
Programming of input and output operations to peripherals requires testing, setting, and
inserting of bit fields in the control registers of the peripherals, which is another application
for bit field instructions. However, control register locations are not memory locations;
therefore, it is not always possible to insert or extract bit fields of a register without affecting
other fields within the register.
Instruction Set Summary
MOTOROLA MC68030 USER’S MANUAL 3-32
Another widely used application for bit field instructions is bit-mapped graphics. Because
byte boundaries are ignored in these areas of memory, the field definitions used with bit field
instructions are very helpful.
3.5.4 Pipeline Synchronization with the Nop Instruction
Although the no operation (NOP) instruction performs no visible operation, it serves an
important purpose. It forces synchronization of the integer unit pipeline by waiting for all
pending bus cycles to complete. All previous integer instructions and floating-point external
operand accesses complete execution before the NOP begins. The NOP instruction does
not synchronize the FPU pipeline; floating-point instructions with floating-point register
operand destinations can be executing when the NOP begins.
MOTOROLA
MC68030 USER’S MANUAL
4-1
SECTION 4
PROCESSING STATES
This section describes the processing states of the MC68030. It describes the functions of
the bits in the supervisor portion of the status register and the actions taken by the processor
in response to exception conditions.
Unless the processor has halted, it is always in either the normal or the exception processing
state. Whenever the processor is executing instructions or fetching instructions or operands,
it is in the normal processing state. The processor is also in the normal processing state
while it is storing instruction results or communicating with a coprocessor.
NOTE
Exception processing refers specifically to the transition from
normal processing of a program to normal processing of system
routines, interrupt routines, and other exception handlers. Ex-
ception processing includes all stacking operations, the fetch of
the exception vector, and filling of the instruction pipe caused by
an exception. It has completed when execution of the first in-
struction of the exception handler routine begins.
The processor enters the exception processing state when an interrupt is acknowledged,
when an instruction is traced or results in a trap, or when some other exceptional condition
arises. Execution of certain instructions or unusual conditions occurring during the execution
of any instructions can cause exceptions. External conditions, such as interrupts, bus errors,
and some coprocessor responses, also cause exceptions. Exception processing provides
an efficient transfer of control to handlers and routines that process the exceptions.
A catastrophic system failure occurs whenever the processor receives a bus error or
generates an address error while in the exception processing state. This type of failure halts
the processor. For example, if during the exception processing of one bus error another bus
error occurs, the MC68030 has not completed the transition to normal processing and has
not completed saving the internal state of the machine, so the processor assumes that the
system is not operational and halts. Only an external reset can restart a halted processor.
(When the processor executes a STOP instruction, it is in a special type of normal
processing state, one without bus cycles. It is stopped, not halted.)
Processing States
4-2
MC68030 USER’S MANUAL
MOTOROLA
4.1 PRIVILEGE LEVELS
The processor operates at one of two levels of privilege: the user level or the supervisor
level. The supervisor level has higher privileges than the user level. Not all processor or
coprocessor instructions are permitted to execute in the lower privileged user level, but all
are available at the supervisor level. This allows a separation of supervisor and user so the
supervisor can protect system resources from uncontrolled access. The processor uses the
privilege level indicated by the S bit in the status register to select either the user or
supervisor privilege level and either the user stack pointer or a supervisor stack pointer for
stack operations. The processor identifies a bus access (supervisor or user mode) via the
function codes so that differentiation between supervisor and user can be maintained. The
memory management unit uses the indication of privilege level to control and translate
memory accesses to protect supervisor code, data, and resources from access by user
programs.
In many systems, the majority of programs execute at the user level. User programs can
access only their own code and data areas and can be restricted from accessing other
information. The operating system typically executes at the supervisor privilege level. It has
access to all resources, performs the overhead tasks for the user level programs, and
coordinates their activities.
4.1.1 Supervisor Privilege Level
The supervisor level is the higher privilege level. The privilege level is determined by the S
bit of the status register; if the S bit is set, the supervisor privilege level applies, and all
instructions are executable. The bus cycles for instructions executed at the supervisor level
are normally classified as supervisor references, and the values of the function codes on
FC0–FC2 refer to supervisor address spaces.
In a multitasking operating system, it is more efficient to have a supervisor stack space
associated with each user task and a separate stack space for interrupt associated tasks.
The MC68030 provides two supervisor stacks, master and interrupt; the M bit of the status
register selects which of the two is active. When the M bit is set to one, supervisor stack
pointer references (either implicit or by specifying address register A7) access the master
stack pointer (MSP). The operating system sets the MSP for each task to point to a task-
related area of supervisor data space. This separates task-related supervisor activity from
asynchronous, I/O-related supervisor tasks that may be only coincidental to the currently
executing task. The master stack (MSP) can separately maintain task control information for
each currently executing user task, and the software updates the MSP when a task switch
is performed, providing an efficient means for transferring task-related stack items. The
other supervisor stack (ISP) can be used for interrupt control information and workspace
area as interrupt handling routines require.
Processing States
MOTOROLA
MC68030 USER’S MANUAL
4-3
When the M bit is clear, the MC68030 is in the interrupt mode of the supervisor privilege
level, and operation is the same as in the MC68000, MC68008, and MC68010 supervisor
mode. (The processor is in this mode after a reset operation.) All supervisor stack pointer
references access the interrupt stack pointer (ISP) in this mode.
The value of the M bit in the status register does not affect execution of privileged
instructions; both master and interrupt modes are at the supervisor privilege level.
Instructions that affect the M bit are MOVE to SR, ANDI to SR, EORI to SR, ORI to SR, and
RTE. Also, the processor automatically saves the M-bit value and clears it in the SR as part
of the exception processing for interrupts.
All exception processing is performed at the supervisor privilege level. All bus cycles
generated during exception processing are supervisor references, and all stack accesses
use the active supervisor stack pointer.
4.1.2 User Privilege Level
The user level is the lower privilege level. The privilege level is determined by the S bit of
the status register; if the S bit is clear, the processor executes instructions at the user
privilege level.
Most instructions execute at either privilege level, but some instructions that have important
system effects are privileged and can only be executed at the supervisor level. For instance,
user programs are not allowed to execute the STOP instruction or the RESET instruction.
To prevent a user program from entering the supervisor privilege level, except in a controlled
manner, instructions that can alter the S bit in the status register are privileged. The TRAP
#n instruction provides controlled access to operating system services for user programs.
Processing States
4-4
MC68030 USER’S MANUAL
MOTOROLA
The bus cycles for an instruction executed at the user privilege level are classified as user
references, and the values of the function codes on FC0-FC2 specify user address spaces.
The memory management unit of the processor, when it is enabled, uses the value of the
function codes to distinguish between user and supervisor activity and to control access to
protected portions of the address space. While the processor is at the user level, references
to the system stack pointer implicitly, or to address register seven (A7) explicitly, refer to the
user stack pointer (USP).
4.1.3 Changing Privilege Level
To change from the user to the supervisor privilege level, one of the conditions that causes
the processor to perform exception processing must occur. This causes a change from the
user level to the supervisor level and can cause a change from the master mode to the
interrupt mode. Exception processing saves the current values of the S and M bits of the
status register (along with the rest of the status register) on the active supervisor stack, and
then sets the S bit, forcing the processor into the supervisor privilege level. When the
exception being processed is an interrupt and the M bit is set, the M bit is cleared, putting
the processor into the interrupt mode. Execution of instructions continues at the supervisor
level to process the exception condition.
To return to the user privilege level, a system routine must execute one of the following
instructions: MOVE to SR, ANDI to SR, EORI to SR, ORI to SR, or RTE. The MOVE, ANDI,
EORI, and ORI to SR and RTE instructions execute at the supervisor privilege level and can
modify the S bit of the status register. After these instructions execute, the instruction
pipeline is flushed and is refilled from the appropriate address space. This is indicated
externally by the assertion of the REFILL signal.
The RTE instruction returns to the program that was executing when the exception occurred.
It restores the exception stack frame saved on the supervisor stack. If the frame on top of
the stack was generated by an interrupt, trap, or instruction exception, the RTE instruction
restores the status register and program counter to the values saved on the supervisor
stack. The processor then continues execution at the restored program counter address and
at the privilege level determined by the S bit of the restored status register. If the frame on
top of the stack was generated by a bus fault (bus error or address error exception), the RTE
instruction restores the entire saved processor state from the stack.
Processing States
MOTOROLA
MC68030 USER’S MANUAL
4-5
4.2 ADDRESS SPACE TYPES
The processor specifies a target address space for every bus cycle with the function code
signals according to the type of access required. In addition to distinguishing between
supervisor/user and program/data, the processor can identify special processor cycles,
such as the interrupt acknowledge cycle, and the memory management unit can control
accesses and translate addresses appropriately. Table 4-1 lists the types of accesses
defined for the MC68030 and the corresponding values of function codes FC0–FC2.
*Address space 3 is reserved for user definition; whereas, 0 and 4
are reserved for future use by Motorola.
The memory locations of user program and data accesses are not predefined. Neither are
the locations of supervisor data space. During reset, the first two long words beginning at
memory location zero in the supervisor program space are used for processor initialization.
No other memory locations are explicitly defined by the MC68030.
A function code of $7 ([FC2:FC0] = 111) selects the CPU address space. This is a special
address space that does not contain instructions or operands but is reserved for special
processor functions. The processor uses accesses in this space to communicate with
external devices for special purposes. For example, all M68000 processors use the CPU
space for interrupt acknowledge cycles. The MC68020 and MC68030 also generate CPU
space accesses for breakpoint acknowledge and coprocessor operations.
Supervisor programs can use the MOVES instruction to access all address spaces,
including the user spaces and the CPU address space. Although the MOVES instruction can
be used to generate CPU space cycles, this may interfere with proper system operation.
Thus, the use of MOVES to access the CPU space should be done with caution.
Table 4-1. Address Space Encodings
FC2 FC1 FC0 Address Space
0 0 0 (Undefined, Reserved)*
0 0 1 User Data Space
0 1 0 User Program Space
0 1 1 (Undefined, Reserved)*
1 0 0 (Undefined, Reserved)*
1 0 1 Supervisor Data Space
1 1 0 Supervisor Program Space
1 1 1 CPU Space
Processing States
4-6
MC68030 USER’S MANUAL
MOTOROLA
4.3 EXCEPTION PROCESSING
An exception is defined as a special condition that pre-empts normal processing. Both
internal and external conditions cause exceptions. External conditions that cause
exceptions are interrupts from external devices, bus errors, coprocessor detected errors,
and reset. Instructions, address errors, tracing, and breakpoints are internal conditions that
cause exceptions. The TRAP, TRAPcc, TRAPV, cpTRAPcc, CHK, CHK2, RTE, and DIV
instructions can all generate exceptions as part of their normal execution. In addition, illegal
instructions, privilege violations, and coprocessor protocol violations cause exceptions.
Exception processing, which is the transition from the normal processing of a program to the
processing required for the exception condition, involves the exception vector table and an
exception stack frame. The following paragraphs describe the vector table and a
generalized exception stack frame. Exception processing is discussed in detail in
Section
8 Exception Processing
.
Coprocessor detected exceptions are discussed in detail in
Section 10 Coprocessor Interface Description
.
4.3.1 Exception Vectors
The vector base register (VBR) contains the base address of the 1024-byte exception vector
table, which consists of 256 exception vectors. Exception vectors contain the memory
addresses of routines that begin execution at the completion of exception processing. These
routines perform a series of operations appropriate for the corresponding exceptions.
Because the exception vectors contain memory addresses, each consists of one long word,
except for the reset vector. The reset vector consists of two long words: the address used
to initialize the interrupt stack pointer and the address used to initialize the program counter.
The address of an exception vector is derived from an 8-bit vector number and the VBR. The
vector numbers for some exceptions are obtained from an external device; others are
supplied automatically by the processor. The processor multiplies the vector number by four
to calculate the vector offset, which it adds to the VBR. The sum is the memory address of
the vector. All exception vectors are located in supervisor data space, except the reset
vector, which is located in supervisor program space. Only the initial reset vector is fixed in
the processor's memory map; once initialization is complete, there are no fixed
assignments. Since the VBR provides the base address of the vector table, the vector table
can be located anywhere in memory; it can even be dynamically relocated for each task that
is executed by an operating system. Details of exception processing are provided in
Section
8 Exception Processing
, and Table 8-1 lists the exception vector assignments.
Processing States
MOTOROLA
MC68030 USER’S MANUAL
4-7
4.3.2 Exception Stack Frame
Exception processing saves the most volatile portion of the current processor context on the
top of the supervisor stack. This context is organized in a format called the exception stack
frame. This information always includes a copy of the status register, the program counter,
the vector offset of the vector, and the frame format field. The frame format field identifies
the type of stack frame. The RTE instruction uses the value in the format field to properly
restore the information stored in the stack frame and to deallocate the stack space. The
general form of the exception stack frame is illustrated in Figure 4-1. Refer to
Section 8
Exception Processing
for a complete list of exception stack frames.
Figure 4-1. General Exception Stack Frame
STATUS REGISTER
FORMAT VECTOR OFFSET
15 12 0
SP
PROGRAM COUNTER
ADDITIONAL PROCESSOR STATE INFORMATION
(2, 6, 12, OR 42 WORDS, IF NEEDED)
MOTOROLA
MC68030 USER’S MANUAL
5-1
SECTION 5
SIGNAL DESCRIPTION
This section contains brief descriptions of the input and output signals in their functional
groups, as shown in Figure 5-1. Each signal is explained in a brief paragraph with reference
to other sections that contain more detail about the signal and the related operations.
Figure 5-1. Functional Signal Groups
DSACK0
FUNCTION CODES
ADDRESS BUS
TRANSFER
SIZE
ASYNCHRONOUS
BUS CONTROL
CACHE
CONTROL
EMULATOR
SUPPORT
SYNCHRONOUS
BUS CONTROL
BUS EXCEPTION
CONTROL
BUS ARBITRATION
CONTROL
INTERRUPT
CONTROL
FC2-FC0
A31-A0
D31-D0
SIZ0
SIZ1
OCS
ECS
R/W
RMC
AS
DS
DBEN
DSACK1
CIIN
CIOUT
CBREQ
CBACK GND (14)
CLK
CDIS
STATUS
REFILL
STERM
BERR
HALT
RESET
IPL0
IPL1
IPL2
IPEND
AVEC
BR
BG
BGACK
V (10)
CC
DATA BUS
MC68EC030
Signal Description
5-2
MC68030 USER’S MANUAL
MOTOROLA
NOTE
In this section and in the remainder of the manual,
assertion
and
negation
are used to specify forcing a signal to a particular
state. In particular, assertion and assert refer to a signal that is
active or true; negation and negate indicate a signal that is inac-
tive or false. These terms are used independently of the voltage
level (high or low) that they represent.
5.1 SIGNAL INDEX
The input and output signals for the MC68030 are listed in Table 5-1. Both the names and
mnemonics are shown along with brief signal descriptions. For more detail on each signal,
refer to the paragraph in this section named for the signal and the reference in that
paragraph to a description of the related operations.
Guaranteed timing specifications for the signals listed in Table 5-1 can be found in
M68030EC/D,
MC68030 Electrical Specifications
.
Table 5-1. Signal Index (Sheet 1 of 2)
Signal Name Mnemonic Function
Function Codes FC0–FC2 3-bit function code used to identify the address space of each bus cycle.
Address Bus A0–A31 32-bit address bus.
Data Bus D0–D31 32-bit data bus used to transfer 8, 16, 24, or 32 bits of data per bus cycle.
Size SIZ0/SIZ1 Indicates the number of bytes remaining to be transferred for this cycle.
These signals, together with A0 and A1, define the active sections of the
data bus.
Operand Cycle Start OCS Identical operation to that of ECS except that OCS is asserted only
during the first bus cycle of an operand transfer.
External Cycle Start ECS Provides an indication that a bus cycle is beginning.
Read/Write R/W Defines the bus transfer as a processor read or write.
Read-Modify-Write Cycle RMC Provides an indicator that the current bus cycle is part of an indivisible
read-modify-write operation.
Address Strobe AS Indicates that a valid address is on the bus.
Data Strobe DS Indicates that valid data is to be placed on the data bus by an external
device or has been placed on the data bus by the MC68030.
Data Buffer Enable DBEN Provides an enable signal for external data buffers.
Signal Description
MOTOROLA
MC68030 USER’S MANUAL
5-3
Table 5-1. Signal Index (Sheet 2 of 2)
Signal Name Mnemonic Function
Data Transfer and
Size Acknowledge DSACK0/
DSACK1 Bus response signals that indicate the requested data transfer operation
is completed. In addition, these two lines indicate the size of the external
bus port on a cycle-by-cycle basis and are used for asynchronous
transfers.
Synchronous
Termination STERM Bus response signal that indicates a port size of 32 bits and that data
may be latched on the next falling clock edge.
Cache Inhibit In CIIN Prevents data from being loaded into the MC68030 instruction and data
caches.
Cache Inhibit Out CIOUT Reflects the CI bit in ATC entries or TTx register; indicates that external
caches should ignore these accesses
Cache Burst Request CBREQ Indicates a burst request for the instruction or data cache.
Cache Burst
Acknowledge CBACK Indicates that the accessed device can operate in burst mode.
Interrupt Priority Level IPL0–IPL2 Provides an encoded interrupt level to the processor.
Interrupt Pending IPEND Indicates that an interrupt is pending.
Autovector AVEC Requests an autovector during an interrupt acknowledge cycle.
Bus Request BR Indicates that an external device requires bus mastership.
Bus Grant BG Indicates that an external device may assume bus mastership.
Bus Grant Acknowledge BGACK Indicates that an external device has assumed bus mastership.
Reset RESET System reset.
Halt HALT Indicates that the processor should suspend bus activity.
Bus Error BERR Indicates that an erroneous bus operation is being attempted.
Cache Disable CDIS Dynamically disables the on-chip cache to assist emulator support.
MMU Disable MMUDIS Dynamically disables the translation mechanism of the MMU.
Pipe Refill REFILL Indicates when the MC68030 is beginning to fill pipeline.
Microsequencer Status STATUS Indicates the state of the microsequencer
Clock CLK Clock input to the processor.
Power Supply V
CC
Power supply.
Ground GND Ground connection
Signal Description
5-4
MC68030 USER’S MANUAL
MOTOROLA
5.2 FUNCTION CODE SIGNALS (FC0
–
FC2)
These three-state outputs identify the address space of the current bus cycle. Table 4-1
shows the relationship of the function code signals to the privilege levels and the address
spaces. Refer to
4.2 Address Space Types
for more information.
5.3 ADDRESS BUS (A0
–
A31)
These three-state outputs provide the address for the current bus cycle, except in the CPU
address space. Refer to
4.2 Address Space Types
for more information on the CPU
address space. A31 is the most significant address signal. Refer to
7.1.2 Address Bus
for
information on the address bus and its relationship to bus operation.
5.4 DATA BUS (D0
–
D31)
These three-state bidirectional signals provide the general-purpose data path between the
MC68030 and all other devices. The data bus can transfer 8, 16, 24, or 32 bits of data per
bus cycle. D31 is the most significant bit of the data bus. Refer to
7.1.4 Data Bus
for more
information on the data bus and its relationship to bus operation.
5.5 TRANSFER SIZE SIGNALS (SIZ0, SIZ1)
These three-state outputs indicate the number of bytes remaining to be transferred for the
current bus cycle. With A0, A1, DSACK0, DSACK1, and STERM, SIZ0 and SIZ1 define the
number of bits transferred on the data bus. Refer to
7.2.1 Dynamic Bus Sizing
for more
information on the size signals and their use in dynamic bus sizing.
Signal Description
MOTOROLA
MC68030 USER’S MANUAL
5-5
5.6 BUS CONTROL SIGNALS
The following signals control synchronous bus transfer operations for the MC68030.
5.6.1 Operand Cycle Start (OCS)
This output signal indicates the beginning of the first external bus cycle for an instruction
prefetch or a data operand transfer. OCS is not asserted for subsequent cycles that are
performed due to dynamic bus sizing or operand misalignment.
7.1.1 Bus Control Signals
for information about the relationship of OCS to bus operation.
5.6.2 External Cycle Start (ECS)
This output signal indicates the beginning of a bus cycle of any type.
7.1.1 Bus Control
Signals
for information about the relationship of ECS to bus operation.
5.6.3 Read/Write (R/W)
This three-state output signal defines the type of bus cycle. A high level indicates a read
cycle; a low level indicates a write cycle. Refer to
7.1.1 Bus Control Signals
for information
about the relationship of R/W to bus operation.
5.6.4 Read-Modify-Write Cycle (RMC)
This three-state output signal identifies the current bus cycle as part of an indivisible read-
modify-write operation; it remains asserted during all bus cycles of the read-modify-write
operation. Refer to
7.1.1 Bus Control Signals
for information about the relationship of RMC
to bus operation.
5.6.5 Address Strobe (AS)
This three-state output indicates that a valid address is on the address bus. The function
code, size, and read/write signals are also valid when AS is asserted. Refer to
7.1.3
Address Strobe
for information about the relationship of AS to bus operation.
Signal Description
5-6
MC68030 USER’S MANUAL
MOTOROLA
5.6.6 Data Strobe (DS)
During a read cycle, this three-state output indicates that an external device should place
valid data on the data bus. During a write cycle, the data strobe indicates that the MC68030
has placed valid data on the bus. During two-clock synchronous write cycles, the MC68030
does not assert DS. Refer to
7.1.5 Data Strobe
for more information about the relationship
of DS to bus operation.
5.6.7 Data Buffer Enable (DBEN)
This output is an enable signal for external data buffers. This signal may not be required in
all systems. The timing of this signal may preclude its use in a system that supports two-
clock synchronous bus cycles. Refer to
7.1.6 Data Buffer Enable
for more information
about the relationship of DBEN to bus operation.
5.6.8 Data Transfer and Size Acknowledge (DSACK0, DSACK1)
These inputs indicate the completion of a requested data transfer operation. In addition, they
indicate the size of the external bus port at the completion of each cycle. These signals apply
only to asynchronous bus cycles. Refer to
7.1.7 Bus Cycle Termination Signals
for more
information on these signals and their relationship to dynamic bus sizing.
5.6.9 Synchronous Termination (STERM)
This input is a bus handshake signal indicating that the addressed port size is 32 bits and
that data is to be latched on the next falling clock edge for a read cycle. This signal applies
only to synchronous operation. Refer to
7.1.7 Bus Cycle Termination Signals
for more
information about the relationship of STERM to bus operation.
Signal Description
MOTOROLA
MC68030 USER’S MANUAL
5-7
5.7 CACHE CONTROL SIGNALS
The following signals relate to the on-chip caches.
5.7.1 Cache Inhibit Input (CIIN)
This input signal prevents data from being loaded into the MC68030 instruction and data
caches. It is a synchronous input signal and is interpreted on a bus-cycle-by-bus-cycle
basis. CIIN is ignored during all write cycles. Refer to
6.1 On-Chip Cache Organization
and Operation
for information on the relationship of CIIN to the on-chip caches.
5.7.2 Cache Inhibit Output (CIOUT)
This three-state output signal reflects the state of the CI bit in the address translation cache
entry for the referenced logical address, indicating that an external cache should ignore the
bus transfer. When the referenced logical address is within an area specified for transparent
translation, the CI bit of the appropriate transparent translation register controls the state of
CIOUT. Refer to
Section 9 Memory Management Unit
for more information about the
address translation cache and transparent translation. Also, refer to
Section 6 On-Chip
Cache Memories
for the effect of CIOUT on the internal caches.
5.7.3 Cache Burst Request (CBREQ)
This three-state output signal requests a burst mode operation to fill a line in the instruction
or data cache. Refer to
6.1.3 Cache Filling
for filling information and
7.3.7 Burst Operation
Cycles
for bus cycle information pertaining to burst mode operations.
5.7.4 Cache Burst Acknowledge (CBACK)
This input signal indicates that the accessed device can operate in the burst mode and can
supply at least one more long word for the instruction or data cache. Refer to
7.3.7 Burst
Operation Cycles
for information about burst mode operation.
Signal Description
5-8
MC68030 USER’S MANUAL
MOTOROLA
5.8 INTERRUPT CONTROL SIGNALS
The following signals are the interrupt control signals for the MC68030.
5.8.1 Interrupt Priority Level Signals
These input signals provide an indication of an interrupt condition and the encoding of the
interrupt level from a peripheral or external prioritizing circuitry. IPL2 is the most significant
bit of the level number. For example, since the IPLn signals are active low, IPL0–IPL2 equal
to $5 corresponds to an interrupt request at interrupt level 2. Refer to
8.1.9 Interrupt
Exceptions
for information on MC68030 interrupts.
5.8.2 Interrupt Pending (IPEND)
This output signal indicates that an interrupt request has been recognized internally and
exceeds the current interrupt priority mask in the status register (SR). This output is for use
by external devices (coprocessors and other bus masters, for example) to predict processor
operation on the following instruction boundaries. Refer to
8.1.9 Interrupt Exceptions
for
interrupt information. Also, refer to
7.4.1 Interrupt Acknowledge Bus Cycles
for bus
information related to interrupts.
5.8.3 Autovector (AVEC)
This input signal indicates that the MC68030 should generate an automatic vector during an
interrupt acknowledge cycle. Refer to
7.4.1.2 Autovector Interrupt Acknowledge Cycle
for more information about automatic vectors.
5.9 BUS ARBITRATION CONTROL SIGNALS
The following signals are the three bus arbitration control signals used to determine which
device in a system is the bus master.
5.9.1 Bus Request (BR)
This input signal indicates that an external device needs to become the bus master. This is
typically a "wire-ORed” input (but does not need to be constructed from open-collector
devices). Refer to
7.7 Bus Arbitration
for more information.
Signal Description
MOTOROLA
MC68030 USER’S MANUAL
5-9
5.9.2 Bus Grant (BG)
This output indicates that the MC68030 will release ownership of the bus master when the
current processor bus cycle completes. Refer to
7.7.2 Bus Grant
for more information.
5.9.3 Bus Grant Acknowledge (BGACK)
This input indicates that an external device has become the bus master. Refer to
7.7.3 Bus
Grant Acknowledge
for more information.
5.10 BUS EXCEPTION CONTROL SIGNALS
The following signals are the bus exception control signals for the MC68030.
5.10.1 Reset (RESET)
This bidirectional open-drain signal is used to initiate a system reset. An external reset signal
resets the MC68030 as well as all external devices. A reset signal from the processor
(asserted as part of the RESET instruction) resets external devices only; the internal state
of the processor is not altered. Refer to
7.8 Reset Operation
for a description of reset bus
operation and 8.1.1 Reset Exception for information about the reset exception.
5.10.2 Halt (HALT)
The halt signal indicates that the processor should suspend bus activity or, when used with
BERR, that the processor should retry the current cycle. Refer to 7.5 Bus Exception
Control Cycles for a description of the effects of HALT on bus operations.
5.10.3 Bus Error (BERR)
The bus error signal indicates that an invalid bus operation is being attempted or, when used
with HALT, that the processor should retry the current cycle. Refer to 7.5 Bus Exception
Control Cycles for a description of the effects of BERR on bus operations.
Signal Description
5-10 MC68030 USER’S MANUAL MOTOROLA
5.11 EMULATOR SUPPORT SIGNALS
The following signals support emulation by providing a means for an emulator to disable the
on-chip caches and memory management unit and by supplying internal status information
to an emulator. Refer to Section 12 Applications Information for more detailed
information on emulation support.
5.11.1 Cache Disable (CDIS)
The cache disable signal dynamically disables the on-chip caches to assist emulator
support. Refer to 6.1 On-Chip Cache Organization and Operation for information about
the caches; refer to Section 12 Applications Information for a description of the use of
this signal by an emulator. CDIS does not flush the data and instruction caches; entries
remain unaltered and become available again when CDIS is negated.
5.11.2 MMU Disable (MMUDIS)
The MMU disable signal dynamically disables the translation of addresses by the MMU.
Refer to 9.4 Address Translation Cache for a description of address translation; refer to
Section 12 Applications Information for a description of the use of this signal by an
emulator. The assertion of MMUDIS does not flush the address translation cache (ATC);
ATC entries become available again when MMUDIS is negated.
5.11.3 Pipeline Refill (REFILL)
The pipeline refill signal indicates that the MC68030 is beginning to refill the internal
instruction pipeline. Refer to Section 12 Applications Information for a description of the
use of this signal by an emulator.
5.11.4 Internal Microsequencer Status (STATUS)
The microsequencer status signal indicates the state of the internal microsequencer. The
varying number of clocks for which this signal is asserted indicates instruction boundaries,
pending exceptions, and the halted condition. Refer to Section 12 Applications
Information for a description of the use of this signal by an emulator.
Signal Description
5-11 MC68030 USER’S MANUAL MOTOROLA
5.12 CLOCK (CLK)
The clock signal is the clock input to the MC68030. It is a TTL-compatible signal. Refer to
Section 12 Applications Information for suggestions on clock generation.
5.13 POWER SUPPLY CONNECTIONS
The MC68030 requires connection to a VCC power supply, positive with respect to ground.
The VCC connections are grouped to supply adequate current for the various sections of the
processor. The ground connections are similarly grouped. Section 14 Ordering
Information and Mechanical Data describes the groupings of VCC and ground
connections, and Section 12 Applications Information describes a typical power supply
interface.
5.14 SIGNAL SUMMARY
Table 5-2 provides a summary of the electrical characteristics of the signals discussed in
this section.
Signal Description
5-12 MC68030 USER’S MANUAL MOTOROLA
Table 5-2. Signal Summary
Signal Function Signal Name Input/Output Active State Three-State
Function Codes FC0–FC2 Output High Yes
Address Bus A0–A31 Output High Yes
Data Bus D0–D31 Input/Output High Yes
Transfer Size SIZ0/SIZ1 Output High Yes
Operand Cycle Start OCS Output Low No
External Cycle Start ECS Output Low No
Read/Write R/W Output High/Low Yes
Read-Modify-Write Cycle RMC Output Low Yes
Address Strobe AS Output Low Yes
Data Strobe DS Output Low Yes
Data Buffer Enable DBEN Output Low Yes
Data Transfer and Size
Acknowledge DSACK0/
DSACK1 Input Low —
Synchronous Termination STERM Input Low —
Cache Inhibit In CIIN Input Low —
Cache Inhibit Out CIOUT Output Low Yes
Cache Burst Request CBREQ Output Low Yes
Cache Burst Acknowledge CBACK Input Low —
Interrupt Priority Level IPL0–IPL2 Input Low —
Interrupt Pending IPEND Output Low No
Autovector AVEC Input Low —
Bus Request BR Input Low —
Bus Grant BG Output Low No
Bus Grant Acknowledge BGACK Input Low —
Reset RESET Input/Output Low No
Halt HALT Input Low —
Bus Error BERR Input Low —
Cache Disable CDIS Input Low —
MMU Disable MMUDIS Input Low —
Pipeline Refill REFILL Output Low No
Microsequencer Status STATUS Output Low No
Clock CLK Input — —
Power Supply VCC Input — —
Ground GND Input — —
MOTOROLA
MC68030 USER’S MANUAL
6-1
SECTION 6
ON-CHIP CACHE MEMORIES
The MC68030 microprocessor includes a 256-byte on-chip instruction cache and a 256-byte
on-chip data cache that are accessed by logical (virtual) addresses. These caches improve
performance by reducing external bus activity and increasing instruction throughput.
Reduced external bus activity increases overall performance by increasing the availability
of the bus for use by external devices (in systems with more than one bus master, such as
a processor and a DMA device) without degrading the performance of the MC68030. An
increase in instruction throughput results when instruction words and data required by a
program are available in the on-chip caches and the time required to access them on the
external bus is eliminated. Additionally, instruction throughput increases when instruction
words and data can be accessed simultaneously.
As shown in Figure 6-1, the instruction cache and the data cache are connected to separate
on-chip address and data buses. The address buses are combined to provide the logical
address to the memory management unit (MMU). The MC68030 initiates an access to the
appropriate cache for the requested instruction or data operand at the same time that it
initiates an access for the translation of the logical address in the address translation cache
of the MMU. When a hit occurs in the instruction or data cache and the MMU validates the
access on a write, the information is transferred from the cache (on a read) or to the cache
and the bus controller (on a write). When a hit does not occur, the MMU translation of the
address is used for an external bus cycle to obtain the instruction or operand. Regardless
of whether or not the required operand is located in one of the on-chip caches, the address
translation cache of the MMU performs logical-to-physical address translation in parallel
with the cache lookup in case an external cycle is required.
On-Chip Cache Memories
6-2
MC68030 USER’S MANUAL
MOTOROLA
Figure 6-1. Internal Caches and the MC68030
MICROSEQUENCER AND
CONTROL
CONTROL
STORE
INSTRUCTION
CACHE
STAGE
B
STAGE
C
STAGE
D
INTERNAL
DATA
BUS
INSTRUCTION PIPE
INSTRUCTION
ADDRESS
BUS
ADDRESS
SECTION
PROGRAM
COUNTER
SECTION
DATA
SECTION
EXECUTION UNIT
MISALIGNMENT
MULTIPLEXER
SIZE
MULTIPLEXER DATA
PADS DATA
BUS
WRITE PENDING
BUFFER PREFETCH PENDING
BUFFER
MICROBUS
CONTROLLER
BUS CONTROLLER
BUS CONTROL
SIGNALS
ADDRESS
BUS
ADDRESS
PADS
ADDRESS
BUS
ADDRESS
DATA
CACHE
DATA
ADDRESS
BUS
CACHE
HOLDING
REGISTER
(CAHR)
ACCESS
CONTROL
UNIT
CONTROL
LOGIC
On-Chip Cache Memories
MOTOROLA
MC68030 USER’S MANUAL
6-3
6.1 ON-CHIP CACHE ORGANIZATION AND OPERATION
Both on-chip caches are 256-byte direct-mapped caches, each organized as 16 lines. Each
line consists of four entries, and each entry contains four bytes. The tag field for each line
contains a valid bit for each entry in the line; each entry is independently replaceable. When
appropriate, the bus controller requests a burst mode operation to replace an entire cache
line. The cache control register (CACR) is accessible by supervisor programs to control the
operation of both caches.
System hardware can assert the cache disable (CDIS) signal to disable both caches. The
assertion of CDIS disables the caches, regardless of the state of the enable bits in CACR.
CDIS is primarily intended for use by in-circuit emulators.
Another input signal, cache inhibit in (CIIN), inhibits caching of data reads or instruction
prefetches on a bus-cycle by bus-cycle basis. Examples of data that should not be cached
are data for I/O devices and data from memory devices that cannot supply a full port width
of data, regardless of the size of the required operand.
Subsequent paragraphs describe how CIIN is used during the filling of the caches.
An output signal, cache inhibit out (CIOUT), reflects the state of the cache inhibit (CI) bit from
the MMU of either the address translation cache entry that corresponds to a specified logical
address or the transparent translation register that corresponds to that address. Whenever
the appropriate CI bit is set for either a read or a write access and an external bus cycle is
required, CIOUT is asserted and the instruction and data caches are ignored for the access.
This signal can also be used by external hardware to inhibit caching in external caches.
Whenever a read access occurs and the required instruction word or data operand is
resident in the appropriate on-chip cache (no external bus cycle is required), the MMU is
completely ignored, unless an invalid translation resides in the MMU at that time (see next
two paragraphs). Therefore, the state of the corresponding CI bits in the MMU are also
ignored. The MMU is used to validate all accesses that require external bus cycles; an
address translation must be available and valid, protections are checked, and the CIOUT
signal is asserted appropriately.
On-Chip Cache Memories
6-4
MC68030 USER’S MANUAL
MOTOROLA
An external access is defined as “cachable” for either the instruction or data cache when all
the following conditions apply:
• The cache is enabled with the appropriate bit in the CACR set.
• The CDIS signal is negated.
• The CIIN signal is negated for the access.
• The CIOUT signal is negated for the access.
• The MMU validates the access.
Because both the data and instruction caches are referenced by logical addresses, they
should be flushed during a task switch or at any time the logical-to-physical address
mapping changes, including when the MMU is first enabled. In addition, if a page descriptor
is currently marked as valid and is later changed to the invalid type (due to a context switch
or a page replacement operation)
entries in the on-chip instruction or data cache
corresponding to the physical page must be first cleared (invalidated)
. Otherwise, if on-chip
cache entries are valid for pages with descriptors in memory marked invalid, processor
operation is unpredictable.
Data read and write accesses to the same address should also have consistent cachability
status to ensure that the data in the cache remains consistent with external memory. For
example, if CIOUT is negated for read accesses within a page and the MMU configuration
is changed so that CIOUT is subsequently asserted for write accesses within the same
page, those write accesses do not update data in the cache, and stale data may result.
Similarly, when the MMU maps multiple logical addresses to the same physical address, all
accesses to those logical addresses should have the same cachability status.
6.1.1 Instruction Cache
The instruction cache is organized with a line size of four long words, as shown in Figure 6-
2. Each of these long words is considered a separate cache entry as each has a separate
valid bit. All four entries in a line have the same tag address. Burst filling all four long words
can be advantageous when the time spent in filling the line is not long relative to the
equivalent bus-cycle time for four nonburst long-word accesses, because of the probability
that the contents of memory adjacent to or close to a referenced operand or instruction is
also required by subsequent accesses. Dynamic RAMs supporting fast access modes
(page, nibble, or static column) are easily employed to support the MC68030 burst mode.
On-Chip Cache Memories
MOTOROLA
MC68030 USER’S MANUAL
6-5
When enabled, the instruction cache is used to store instruction prefetches (instruction
words and extension words) as they are requested by the CPU. Instruction prefetches are
normally requested from sequential memory addresses except when a change of program
flow occurs (e.g., a branch taken) or when an instruction is executed that can modify the
status register, in which cases the instruction pipe is automatically flushed and refilled. The
output signal REFILL indicates this condition. For more information on the operation of this
signal, refer to
Section 12 Applications Information
.
In the instruction cache, each of the 16 lines has a tag consisting of the 24 most significant
logical address bits, the FC2 function code bit (used to distinguish between user and
supervisor accesses), and the four valid bits (one corresponding to each long word). Refer
to Figure 6-2 for the instruction cache organization. Address bits A7–A4 select one of 16
lines and its associated tag. The comparator compares the address and function code bits
in the selected tag with address bits A31–A8 and FC2 from the internal prefetch request to
determine if the requested word is in the cache. A cache hit occurs when there is a tag match
and the corresponding valid bit (selected by A3–A2) is set. On a cache hit, the word selected
by address bit A1 is supplied to the instruction pipe.
When the address and function code bits do not match or the requested entry is not valid, a
miss occurs. The bus controller initiates a long-word prefetch operation for the required
Figure 6-2. On-Chip Instruction Cache Organization
F F F
CCC 3 222211111111110000000000
210 1 32 01 98765432109876543210
COMPARATOR
TAG
1 OF 16
SELECT
VALID
TAG REPLACE
INDEX
TAG
LINE HIT
DATA FROM INSTRUCTION
CACHE DATA BUS
CACHE CONTROL LOGIC
V V VV
ACCESS ADDRESS
DATA TO INSTRUCTION
CACHE HOLDING REGISTER
ENTRY HIT
A
LONG-WORD
SELECT
CACHE SIZE = 64 (LONG WORDS)
LINE SIZE = 4 (LONG WORDS)
SET SIZE = 1
AAAAAAAAAAAAAAAAAAAAAAAA
On-Chip Cache Memories
6-6
MC68030 USER’S MANUAL
MOTOROLA
instruction word and loads the cache entry, provided the entry is cachable. A burst mode
operation may be requested to fill an entire cache line. If the function code and address bits
match and the corresponding long word is not valid (but one or more of the other three valid
bits for that line are set) a single entry fill operation replaces the required long word only,
using a normal prefetch bus cycle or cycles (no burst).
6.1.2 Data Cache
The data cache stores data references to any address space except CPU space (FC=$7),
including those references made with PC relative addressing modes and accesses made
with the MOVES instruction. Operation of the data cache is similar to that of the instruction
cache, except for the address comparison and cache filling operations. The tag of each line
in the data cache contains function code bits FC0, FC1, and FC2 in addition to address bits
A31–A8. The cache control circuitry selects the tag using bits A7–A4 and compares it to the
corresponding bits of the access address to determine if a tag match has occurred. Address
bits A3–A2 select the valid bit for the appropriate long word in the cache to determine if an
entry hit has occurred. Misaligned data transfers may span two data cache entries. In this
case, the processor checks for a hit one entry at a time. Therefore, it is possible that a
portion of the access results in a hit and a portion results in a miss. The hit and miss are
treated independently. Figure 6-3 illustrates the organization of the data cache.
The operation of the data cache differs for read and write cycles. A data read cycle operates
exactly like an instruction cache read cycle; when a miss occurs, an external cycle is initiated
to obtain the operand from memory, and the data is loaded into the cache if the access is
cachable. In the case of a misaligned operand that spans two cache entries, two long words
are required from memory. Burst mode operation may also be initiated to fill an entire line of
the data cache. Read accesses from the CPU address space and address translation table
search accesses are not stored in the data cache.
The data cache on the MC68030 is a writethrough cache. When a hit occurs on a write cycle,
the data is written both to the cache and to external memory (provided the MMU validates
the access), regardless of the operand size and even if the cache is frozen. If the MMU
determines that the access is invalid, the write is aborted, the corresponding entry is
invalidated, and a bus error exception is taken. Since the write to the cache completes
before the write to external memory, the cache contains the new value even if the external
write terminates in a bus error. The value in the data cache might be used by another
instruction before the external write cycle has completed, although this should not have any
adverse consequences. Refer to
7.6 Bus Synchronization
for the details of bus
synchronization.
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6-7
6.1.2.1 WRITE ALLOCATION.
The supervisor program can configure the data cache for
either of two types of allocation for data cache entries that miss on write cycles. The state
of the write allocation (WA) bit in the cache control register specifies either no write
allocation or write allocation with partial validation of the data entries in the cache on writes.
When no write allocation is selected (WA=0), write cycles that miss do not alter the data
cache contents. In this mode, the processor does not replace entries in the cache during
write operations. The cache is updated only during a write hit.
When write allocation is selected (WA=1), the processor always updates the data cache on
cachable write cycles, but only validates an updated entry that hits or an entry that is
updated with long-word data that is long-word aligned. When a tag miss occurs on a write
of long-word data that is long-word aligned, the corresponding tag is replaced, and only the
long word being written is marked as valid. The other three entries in the cache line are
invalidated when a tag miss occurs on a misaligned long-word write or on a byte or word
write, the data is not written in the cache, the tag is unaltered, and the valid bit(s) are cleared.
Thus, an aligned long-word data write may replace a previously valid entry; whereas, a
misaligned data write or a write of data that is not long word may invalidate a previously valid
entry or entries.
Figure 6-3. On-Chip Data Cache Organization
DATA FROM DATA
CACHE DATA BUS
CACHE CONTROL LOGIC
DATA TO
EXECUTION UNIT
F F F
CCC 3 222211111111110000000000
210 1 32 01 98765432109876543210
COMPARATOR
TAG
1 OF 16
SELECT
VALID
TAG REPLACE
INDEX
TAG
LINE HIT
V V VV
ACCESS ADDRESS
ENTRY HIT
A
LONG-WORD
SELECT
CACHE SIZE = 64 (LONG WORDS)
LINE SIZE = 4 (LONG WORDS)
SET SIZE = 1
AAAAAAAAAAAAAAAAAAAAAAAA
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MOTOROLA
Write allocation eliminates stale data that may reside in the cache because of either of two
unique situations: multiple mapping of two or more logical addresses to one physical
address within the same task or allowing the same physical location to be accessed by both
supervisor and user mode cycles. Stale data conditions can arise when operating in the no-
write-allocation mode and all the following conditions are satisfied:
• Multiple mapping (object aliasing) is allowed by the operating system.
• A read cycle loads a value for an “aliased” physical address into the data cache.
• A write cycle occurs, referencing the same aliased physical object as above but using
a different logical address, causing a cache miss and no update to the cache (has the
same page offset).
• The physical object is then read using the first alias, which provides stale data from the
cache.
In this case, the data in the cache no longer matches that in physical memory and is stale.
Since the write-allocation mode updates the cache during write cycles, the data in the cache
remains consistent with physical memory. Note that when CIOUT is asserted, the data
cache is completely ignored, even on write cycles operating in the write-allocation mode.
Also note that since the CIIN signal is ignored on write cycles, cache entries may be created
for noncachable data (when CIIN is asserted on a write) when operating in the write-
allocation mode. Figure 6-4 shows the manner in which each mode operates in five different
situations.
Figure 6-4. No-Write-Allocation and Write-Allocation Mode Examples
USER DATA, $000010 b0-b3, V0 = 1 b4-b7, V1 = 0 b8-bB, V2 = 1 bC-bF, V3 = 1
LINE
SELECT
($5)
LOGICAL ADDRESS = FC2-FC0, A31-A8, A7-A4, A3-A2
TAG'
TAG
EXAMPLE 1:
USER WORD WRITE OF b2'-b3' to $00001052
(CACHE HIT, ALWAYS UPDATE CACHE AND MEMORY)
EXAMPLE 2:
USER LONG-WORD WRITE OF b6'-b9' to $00001056
(TAG MATCH, LONG-WORD DATA, MISALIGNED,
b6-b7 RESULT IN A CACHE MISS,
b8-b9 RESULT IN A CACHE HIT)
A) START EXTERNAL CYCLE
B) b2-b3 b2'-b3'
NO WRITE ALLOCATE
A) START EXTERNAL CYCLE
B) b8-b9 b8'-b9'
A) START EXTERNAL CYCLE
B) b2-b3 b2'-b3'
WRITE ALLOCATE
A) START EXTERNAL CYCLE
B) b8-b9 b8'-b9'
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6-9
6.1.2.2 READ-MODIFY-WRITE ACCESSES.
The read portion of a read-modify-write cycle
is always forced to miss in the data cache. However, if the system allows internal caching
of read-modify-write cycle operands (CIOUT and CIIN both negated), the processor either
uses the data read from memory to update a matching entry in the data cache or creates a
new entry with the read data in the case of no matching entry. The write portion of a read-
modify-write operation also updates a matching entry in the data cache. In the case of a
cache miss on the write, the allocation of a new cache entry for the data being written is
controlled by the WA bit. Table search accesses, however, are completely ignored by the
data cache; it is never updated for a table search access.
6.1.3 Cache Filling
The bus controller can load either cache in either of two ways:
• Single entry mode
• Burst fill mode
In the single entry mode, the bus controller loads a single long-word entry of a cache line.
In the burst fill mode, an entire line (four long words) can be filled. Refer to
Section 7 Bus
Operation
for detailed information about the bus cycles required for both modes.
6.1.3.1 SINGLE ENTRY MODE.
When a cachable access is initiated and a burst mode
operation is not requested by the MC68030 or is not supported by external hardware, the
bus controller transfers a single long word for the corresponding cache entry. An entire long
word is required. If the port size of the responding device is smaller than 32 bits, the
MC68030 executes all bus cycles necessary to fill the long word.
When a device cannot supply its entire port width of data, regardless of the size of the
transfer, the responding device must consistently assert the cache inhibit input (CIIN) signal.
For example, a 32-bit port must always supply 32 bits, even for 8- and 16-bit transfers; a 16-
bit port must supply 16 bits, even for 8-bit transfers. The MC68030 assumes that a 32-bit
termination signal for the bus cycle indicates availability of 32 valid data bits, even if only 16
or 8 bits are requested. Similarly, the processor assumes that a 16-bit termination signal
indicates that all 16 bits are valid. If the device cannot supply its full port width of data, it must
assert CIIN for all bus cycles corresponding to a cache entry.
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When a cachable read cycle provides data with both CIIN and BERR negated, the MC68030
attempts to fill the cache entry. Figure 6-5 shows the organization of a line of data in the
caches. The notation b0, b1, b2, and so forth identifies the bytes within the line. For each
entry in the line, a valid bit in the associated tag corresponds to a long-word entry to be
loaded. Since a single valid bit applies to an entire long word, a single entry mode operation
must provide a full 32 bits of data. Ports less than 32 bits wide require several read cycles
for each entry.
Figure 6-5 shows an example of a byte data operand read cycle starting at byte address $03
from an 8-bit port. Provided the data item is cachable, this operation results in four bus
cycles. The first cycle requested by the MC68030 reads a byte from address $03. The 8-bit
DSACKx response causes the MC68030 to fetch the remainder of the long word starting at
address $00. The bytes are latched in the following order: b3, b0, b1, and b2. Note that
during cache loading operations, devices must indicate the same port size consistently
throughout all cycles for that long-word entry in the cache.
Figure 6-6 shows the access of a byte data operand from a 16-bit port. This operation
requires two read cycles. The first cycle requests the byte at address $03. If the device
responds with a 16-bit DSACKx encoding, the word at address $02 (including the requested
byte) is accepted by the MC68030. The second cycle requests the word at address $00.
Since the device again responds with a 16-bit DSACKx encoding, the remaining two bytes
of the long word are latched, and the cache entry is filled.
With a 32-bit port, the same operation is shown in Figure 6-7. Only one read cycle is
required. All four bytes (including the requested byte) are latched during the cycle.
If a requested access is misaligned and spans two cache entries, the bus controller attempts
to fill both associated long-word cache entries. An example of this is an operand request for
a long word on an odd-word boundary. The MC68030 first fetches the initial byte(s) of the
operand (residing in the first long word) and then requests the remaining bytes to fill that
cache entry (if the port size is less than 32 bits) before it requests the remainder of the
operand and corresponding long word to fill the second cache entry. If the port size is 32
bits, the processor performs two accesses, one for each cache entry.
(UNABLE TO LOCATE ART)
Figure 6-5. Single Entry Mode Operation — 8-Bit Port
(UNABLE TO LOCATE ART)
Figure 6-6. Single Entry Mode Operation — 16-Bit Port
(UNABLE TO LOCATE ART)
Figure 6-7. Single Entry Mode Operation — 32-Bit Port
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Figure 6-8 shows a misaligned access of a long word at address $06 from an 8-bit port
requiring eight bus cycles to complete. Reading this long-word operand requires eight read
cycles, since accesses to all eight addresses return 8-bit port-size encodings. These cycles
fetch the two cache entries that the requested long-word spans. The first cycle requests a
long word at address $06 and accepts the first requested byte (b6). The subsequent
transfers of the first long word are performed in the following order: b7, b4, b5. The
remaining four read cycles transfer the four bytes of the second cache entry. The sequence
of access for the entire operation is b6, b7, b4, b5, b8, b9, bA, and bB.
The next example, shown in Figure 6-9, is a read of a misaligned long-word operand from
devices that return 16-bit DSACKx encodings. The processor accepts the first portion of the
operand, the word from address $06, and requests a word from address $04 to fill the cache
entry. Next, the processor reads the word at address $08, the second portion of the operand,
and stores it in the cache also. Finally, the processor accesses the word at $0A to fill the
second long-word cache entry.
Two read cycles are required for a misaligned long-word operand transfer from devices that
return 32-bit DSACKx encodings. As shown in Figure 6-10, the first read cycle requests the
long word at address $06 and latches the long word at address $04. The second read cycle
requests and latches the long word corresponding to the second cache entry at address
$08. Two read cycles are also required if STERM is used to indicate a 32-bit port instead of
the 32-bit DSACKx encoding.
If all bytes of a long word are cachable, CIIN must be negated for all bus cycles required to
fill the entry. If any byte is not cachable, CIIN must be asserted for all corresponding bus
cycles. The assertion of the CIIN signal prevents the caches from being updated during read
cycles. Write cycles (including the write portion of a read-modify-write cycle) ignore the
assertion of the CIIN signal and may cause the data cache to be altered, depending on the
state of the cache (whether or not the write cycle hits), the state of the WA bit in the CACR,
and the conditions indicated by the MMU.
The occurrence of a bus error while attempting to load a cache entry aborts the entry fill
operation but does not necessarily cause a bus error exception. If the bus error occurs on a
read cycle for a portion of the required operand (not the remaining bytes of the cache entry)
to be loaded into the data cache, the processor immediately takes a bus error exception. If
(UNABLE TO LOCATE ART)
Figure 6-8. Single Entry Mode Operation —
Misaligned Long Word and 8-Bit Port
(UNABLE TO LOCATE ART)
Figure 6-9. Single Entry Mode Operation —
Misaligned Long Word and 16-Bit Port
(UNABLE TO LOCATE ART)
Figure 6-10. Single Entry Mode Operation —
Misaligned Long Word and 32-Bit DSACKx Port
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MOTOROLA
the read cycle in error is made only to fill the data cache (the data is not part of the target
operand), no exception occurs, but the corresponding entry is marked invalid. For the
instruction cache, the processor marks the entry as invalid, but only takes an exception if
the execution unit attempts to use the instruction word(s).
6.1.3.2 BURST MODE FILLING.
Burst mode filling is enabled by bits in the cache control
register. The data burst enable bit must be set to enable burst filling of the data cache.
Similarly, the instruction burst enable bit must be set to enable burst filling of the instruction
cache. When burst filling is enabled and the corresponding cache is enabled, the bus
controller requests a burst mode fill operation in either of these cases:
• A read cycle for either the instruction or data cache misses due to the indexed tag not
matching.
• A read cycle tag matches, but all long words in the line are invalid.
The bus controller requests a burst mode fill operation by asserting the cache burst request
signal (CBREQ). The responding device may sequentially supply one to four long words of
cachable data, or it may assert the cache inhibit input signal (CIIN) when the data in a long
word is not cachable. If the responding device does not support the burst mode and it
terminates cycles with STERM, it should not acknowledge the request with the assertion of
the cache burst acknowledge (CBACK) signal. The MC68030 ignores the assertion of
CBACK during cycles terminated with DSACKx.
The cache burst request signal (CBREQ) requests burst mode operation from the
referenced external device. To operate in the burst mode, the device or external hardware
must be able to increment the low-order address bits if required, and the current cycle must
be a 32-bit synchronous transfer (STERM must be asserted) as described in
Section 7 Bus
Operation
. The device must also assert CBACK (at the same time as STERM) at the end
of the cycle in which the MC68030 asserts CBREQ. CBACK causes the processor to
continue driving the address and bus control signals and to latch a new data value for the
next cache entry at the completion of each subsequent cycle (as defined by STERM), for a
total of up to four cycles (until four long words have been read).
When a cache burst is initiated, the first cycle attempts to load the cache entry
corresponding to the instruction word or data item explicitly requested by the execution unit.
The subsequent cycles are for the subsequent entries in the cache line. In the case of a
misaligned transfer when the operand spans two cache entries within a cache line, the first
cycle corresponds to the cache entry containing the portion of the operand at the lower
address.
Figure 6-11 illustrates the four cycles of a burst operation and shows that the second, third,
and fourth cycles are run in burst mode. A distinction is made between the first cycle of a
burst operation and the subsequent cycles because the first cycle is requested by the
microsequencer and the burst fill cycles are requested by the bus controller. Therefore,
when data from the first cycle is returned, it is immediately available for the execution unit
(EU). However, data from the burst fill cycles is not available to the EU until the burst
operation is complete. Since the microsequencer makes two separate requests for
misaligned data operands, only the first portion of the misaligned operand returned during a
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6-13
burst operation is available to the EU after the first cycle is complete. The microsequencer
must wait for the burst operation to complete before requesting the second portion of the
operand. Normally, the request for the second portion results in a data cache hit unless the
second cycle of the burst operation terminates abnormally.
The bursting mechanism allows addresses to wrap around so that the entire four long words
in the cache line can be filled in a single burst operation, regardless of the initial address and
operand alignment. Depending on the structure of the external memory system, address bits
A2 and A3 may have to be incremented externally to select the long words in the proper
order for loading into the cache. The MC68030 holds the entire address bus constant for the
duration of the burst cycle. Figure 6-12 shows an example of this address wraparound. The
initial cycle is a long-word access from address $6. Because the responding device returns
CBACK and STERM (signaling a 32-bit port), the entire long word at base address $04 is
transferred. Since the initial address is $06 when CBREQ is asserted, the next entry to be
burst filled into the cache should correspond to address $08, then $0C, and last, $00. This
addressing is compatible with existing nibble-mode dynamic RAMs, and can be supported
by page and static column modes with an external modulo 4 counter for A2 and A3.
The MC68030 does not assert CBREQ during the first portion of a misaligned access if the
remainder of the access does not correspond to the same cache line. Figure 6-13 shows an
example in which the first portion of a misaligned access is at address $0F. With a 32-bit
port, the first access corresponds to the cache entry at address $0C, which is filled using a
single-entry load operation. The second access, at address $10 corresponding to the
second cache line, requests a burst fill and the processor asserts CBREQ. During this burst
operation, long words $10, $14, $18, and $1C are all filled in that order.
Figure 6-11. Burst Operation Cycles and Burst Mode
(UNABLE TO LOCATE ART)
Figure 6-12. Burst Filling Wraparound Example
(UNABLE TO LOCATE ART)
Figure 6-13. Deferred Burst Filling Example
FIRST ACCESS OF BURST
OPERATION REQUIRED
OPERAND OR PREFETCH BURST FILL CYCLE BURST FILL CYCLE BURST FILL CYCLE
CYCLE 1 CYCLE 2 CYCLE 3 CYCLE 4
BURST MODE
REQUESTED AND
ACKNOWLEDGED BURST MODE BEGINS HERE
BURST OPERATION
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The processor does not assert CBREQ if any of the following conditions exist:
• The appropriate cache is not enabled
• Burst filling for the cache is not enabled
• The cache freeze bit for the appropriate cache is set
• The current operation is the read portion of a read-modify-write operation
• The MMU has inhibited caching for the current page
• The cycle is for the first access of an operand that spans two cache lines (crosses a
modulo 16 boundary)
Additionally, the assertion of CIIN and BERR and the premature negation of CBACK affect
burst operation as described in the following paragraphs.
The assertion of CIIN during the first cycle of a burst operation causes the data to be latched
by the processor, and if the requested operand is aligned (the entire operand is latched in
the first cycle), the data is passed on to the instruction pipe or execution unit. However, the
data is not loaded into its corresponding cache. In addition, the MC68030 negates CBREQ,
and the burst operation is aborted. If a portion of the requested operand remains to be read
(due to misalignment), a second read cycle is initiated at the appropriate address with
CBREQ negated.
The assertion of CIIN during the second, third, or fourth cycle of a burst operation prevents
the data during that cycle from being loaded into the appropriate cache and causes CBREQ
to negate, aborting the burst operation. However, if the data for the cycle contains part of
the requested operand, the execution unit uses that data.
The premature negation of the CBACK signal during the burst operation causes the current
cycle to complete normally, loading the data successfully transferred into the appropriate
cache. However, the burst operation aborts and CBREQ negates.
A bus error occurring during a burst operation also causes the burst operation to abort. If the
bus error occurs during the first cycle of a burst (i.e., before burst mode is entered), the data
read from the bus is ignored, and the entire associated cache line is marked “invalid”. If the
access is a data cycle, exception processing proceeds immediately. If the cycle is for an
instruction fetch, a bus error exception is made pending. This bus error is processed only if
the execution unit attempts to use either instruction word. Refer to
11.2.2 Instruction Pipe
for more information about pipeline operation.
For either cache, when a bus error occurs after the burst mode has been entered (that is,
on the second cycle or later), the cache entry corresponding to that cycle is marked invalid,
but the processor does not take an exception (the microsequencer has not yet requested
the data). In the case of an instruction cache burst, the data from the aborted cycle is
completely ignored. Pending instruction prefetches are still pending and are subsequently
run by the processor. If the second cycle is for a portion of a misaligned data operand fetch
and a bus error occurs, the processor terminates the burst operation and negates CBREQ.
Once the burst terminates, the microsequencer requests a read cycle for the second portion.
Since the burst terminated abnormally for the second cycle of the burst, the data cache
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results in a miss, and a second external cycle is required. If BERR is again asserted, the
MC68030 then takes an exception.
On the initial access of a burst operation, a “retry'“(indicated by the assertion of BERR and
HALT) causes the processor to retry the bus cycle and assert CBREQ again. However,
signaling a retry with simultaneous BERR and HALT during the second, third, or fourth cycle
of a burst operation does not cause a retry operation, even if the requested operand is
misaligned. Assertion of BERR and HALT during burst fill cycles of a burst operation causes
independent bus error and halt operations. The processor remains halted until HALT is
negated, and then handles the bus error as described in the previous paragraphs.
6.2 CACHE RESET
When a hardware reset of the processor occurs, all valid bits of both caches are cleared.
The cache enable bits, burst enable bits, and the freeze bits in the cache control register
(CACR) for both caches (refer to Figure 6-14) are also cleared, effectively disabling both
caches. The WA bit in the CACR is also cleared.
6.3 CACHE CONTROL
Only the MC68030 cache control circuitry can directly access the cache arrays, but the
supervisor program can set bits in the CACR to exercise control over cache operations. The
supervisor also has access to the cache address register (CAAR), which contains the
address for a cache entry to be cleared.
6.3.1 Cache Control Register
The CACR, shown in Figure 6-14, is a 32-bit register that can be written or read by the
MOVEC instruction or indirectly modified by a reset. Five of the bits (4-0) control the
instruction cache; six other bits (13-8) control the data cache. Each cache is controlled
independently of the other, although a similar operation can be performed for both caches
by a single MOVEC instruction. For example, loading a long word in which bits 3 and 11 are
set into the CACR clears both caches. Bits 31-14 and 7-5 are reserved for Motorola
definition. They are currently read as zeros and are ignored when written. For future
compatibility, writes should not set these bits.
WA = Write Allocate
DBE = Data Burst Enable
CD = Clear Data Cache
CED = Clear Entry in Data Cache
FD = Freeze Data Cache
ED = Freeze Data Cache
IBE = Instruction Burst Enable
CI = Clear Instruction Cache
CEI = Clear Entry in Instruction Cache
FI = Freeze Instruction Cache
EI = Enable Instruction Cache
Figure 6-14. Cache Control Register
31 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
000000000000000000 WA DBE CD CED FD ED 0 0 0 IBE CI CEI FI EI
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6.3.1.1 WRITE ALLOCATE.
Bit 13, the WA bit, is set to select the write-allocation mode
(refer to
6.1.2.1 Write Allocation
) for write cycles. Clearing this bit selects the no-write-
allocation mode. A reset operation clears this bit. The supervisor should set this bit when it
shares data with the user task or when any task maps multiple logical addresses to one
physical address. If the data cache is disabled or frozen, the WA bit is ignored.
6.3.1.2 DATA BURST ENABLE.
Bit 12, the DBE bit, is set to enable burst filling of the data
cache. Operating systems and other software set this bit when burst filling of the data cache
is desired. A reset operation clears the DBE bit.
6.3.1.3 CLEAR DATA CACHE.
Bit 11, the CD bit, is set to clear all entries in the data cache.
Operating systems and other software set this bit to clear data from the cache prior to a
context switch. The processor clears all valid bits in the data cache at the time a MOVEC
instruction loads a one into the CD bit of the CACR. The CD bit is always read as a zero.
6.3.1.4 CLEAR ENTRY IN DATA CACHE.
Bit 10, the CED bit, is set to clear an entry in the
data cache. The index field of the CAAR (see Figure 6-15) corresponding to the index and
long-word select portion of an address specifies the entry to be cleared. The processor
clears only the specified long word by clearing the valid bit for the entry at the time a MOVEC
instruction loads a one into the CED bit of the CACR, regardless of the states of the ED and
FD bits. The CED bit is always read as a zero.
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6.3.1.5 FREEZE DATA CACHE.
Bit 9, the FD bit, is set to freeze the data cache. When the
FD bit is set and a miss occurs during a read or write of the data cache, the indexed entry
is not replaced. However, write cycles that hit in the data cache cause the entry to be
updated even when the cache is frozen. When the FD bit is clear, a miss in the data cache
during a read cycle causes the entry (or line) to be filled, and the filling of entries on writes
that miss are then controlled by the WA bit. A reset operation clears the FD bit.
6.3.1.6 ENABLE DATA CACHE.
Bit 8, the ED bit, is set to enable the data cache. When it
is cleared, the data cache is disabled. A reset operation clears the ED bit. The supervisor
normally enables the data cache, but it can clear ED for system debugging or emulation, as
required. Disabling the data cache does not flush the entries. If it is enabled again, the
previously valid entries remain valid and can be used.
6.3.1.7 INSTRUCTION BURST ENABLE.
Bit 4, the IBE bit, is set to enable burst filling of
the instruction cache. Operating systems and other software set this bit when burst filling of
the instruction cache is desired. A reset operation clears the IBE bit.
6.3.1.8 CLEAR INSTRUCTION CACHE.
Bit 3, the CI bit, is set to clear all entries in the
instruction cache. Operating systems and other software set this bit to clear instructions from
the cache prior to a context switch. The processor clears all valid bits in the instruction cache
at the time a MOVEC instruction loads a one into the CI bit of the CACR. The CI bit is always
read as a zero.
6.3.1.9 CLEAR ENTRY IN INSTRUCTION CACHE.
Bit 2, the CEI bit, is set to clear an
entry in the instruction cache. The index field of the CAAR (see Figure 6-15) corresponding
to the index and long-word select portion of an address specifies the entry to be cleared.
The processor clears only the specified long word by clearing the valid bit for the entry at the
time a MOVEC instruction loads a one into the CEI bit of the CACR, regardless of the states
of the EI and FI bits. The CEI bit is always read as a zero.
On-Chip Cache Memories
6-18
MC68030 USER’S MANUAL
MOTOROLA
6.3.1.10 FREEZE INSTRUCTION CACHE.
Bit 1, the FI bit, is set to freeze the instruction
cache. When the FI bit is set and a miss occurs in the instruction cache, the entry (or line)
is not replaced. When the FI bit is cleared to zero, a miss in the instruction cache causes the
entry (or line) to be filled. A reset operation clears the FI bit.
6.3.1.11 ENABLE INSTRUCTION CACHE.
Bit 0, the EI bit, is set to enable the instruction
cache. When it is cleared, the instruction cache is disabled. A reset operation clears the EI
bit. The supervisor normally enables the instruction cache, but it can clear EI for system
debugging or emulation, as required. Disabling the instruction cache does not flush the
entries. If it is enabled again, the previously valid entries remain valid and may be used.
6.3.2 Cache Address Register
The CAAR is a 32-bit register shown in Figure 6-15. The index field (bits 7-2) contains the
address for the “clear cache entry” operations. The bits of this field correspond to bits 7-2 of
addresses; they specify the index and a long word of a cache line. Although only the index
field is used currently, all 32 bits of the register are implemented and are reserved for use
by Motorola.
Figure 6-15. Cache Address Register
31 8 7 2 1 0
CACHE FUNCTION ADDRESS INDEX
MOTOROLA
MC68030 USER’S MANUAL
7-1
SECTION 7
BUS OPERATION
This section provides a functional description of the bus, the signals that control it, and the
bus cycles provided for data transfer operations. It also describes the error and halt
conditions, bus arbitration, and the reset operation. Operation of the bus is the same
whether the processor or an external device is the bus master; the names and descriptions
of bus cycles are from the point of view of the bus master. For exact timing specifications,
refer to
Section 13 Electrical Characteristics
.
The MC68030 architecture supports byte, word, and long-word operands, allowing access
to 8-, 16-, and 32-bit data ports through the use of asynchronous cycles controlled by the
data transfer and size acknowledge inputs (DSACK0 and DSACK1).
Synchronous bus cycles controlled by the synchronous termination signal (STERM) can
only be used to transfer data to and from 32-bit ports.
The MC68030 allows byte, word, and long-word operands to be located in memory on any
byte boundary. For a misaligned transfer, more than one bus cycle may be required to
complete the transfer, regardless of port size. For a port less than 32 bits wide, multiple bus
cycles may be required for an operand transfer due to either misalignment or a port width
smaller than the operand size. Instruction words and their associated extension words must
be aligned on word boundaries. The user should be aware that misalignment of word or
long-word operands can cause the MC68030 to perform multiple bus cycles for the operand
transfer; therefore, processor performance is optimized if word and long-word memory
operands are aligned on word or long-word boundaries, respectively.
7.1 BUS TRANSFER SIGNALS
The bus transfers information between the MC68030 and an external memory, coprocessor,
or peripheral device. External devices can accept or provide 8 bits, 16 bits, or 32 bits in
parallel and must follow the handshake protocol described in this section. The maximum
number of bits accepted or provided during a bus transfer is defined as the port width. The
MC68030 contains an address bus that specifies the address for the transfer and a data bus
that transfers the data. Control signals indicate the beginning of the cycle, the address space
and the size of the transfer, and the type of cycle. The selected device then controls the
length of the cycle with the signal(s) used to terminate the cycle. Strobe signals, one for the
address bus and another for the data bus, indicate the validity of the address and provide
timing information for the data.
Bus Operation
7-2
MC68030 USER’S MANUAL
MOTOROLA
The bus can operate in an asynchronous mode identical to the MC68020 bus for any port
width. The bus and control input signals used for asynchronous operation are internally
synchronized to the MC68030 clock, introducing a delay. This delay is the time period
required for the MC68030 to sample an asynchronous input signal, synchronize the input to
the internal clocks of the processor, and determine whether it is high or low. Figure 7-1
shows the relationship between the clock signal and the associated internal signal of a
typical asynchronous input.
Furthermore, for all asynchronous inputs, the processor latches the level of the input during
a sample window around the falling edge of the clock signal. This window is illustrated in
Figure 7-2. To ensure that an input signal is recognized on a specific falling edge of the
clock, that input must be stable during the sample window. If an input makes a transition
during the window time period, the level recognized by the processor is not predictable;
however, the processor always resolves the latched level to either a logic high or low before
using it. In addition to meeting input setup and hold times for deterministic operation, all input
signals must obey the protocols described in this section.
Figure 7-1. Relationship between External and Internal Signals
SYNC DELAY
CLK
EXT
INT
Bus Operation
MOTOROLA
MC68030 USER’S MANUAL
7-3
A device with a 32-bit port size can also provide a synchronous mode transfer. In
synchronous operation, input signals are externally synchronized to the processor clock,
and the synchronizing delay is not incurred.
Synchronous inputs (STERM, CBACK, and CIIN) must remain stable during a sample
window for all rising edges of the clock during a bus cycle (i.e., while address strobe (AS) is
asserted), regardless of when the signals are asserted or negated, to ensure proper
operation. This sample window is defined by the synchronous input setup and hold times
(see MC68030EC/D,
MC68030 Electrical Specifications
).
7.1.1 Bus Control Signals
The external cycle start (ECS) signal is the earliest indication that the processor is initiating
a bus cycle. The MC68030 initiates a bus cycle by driving the address, size, function code,
read/write, and cache inhibit-out outputs and by asserting ECS. However, if the processor
finds the required program or data item in an on-chip cache, if a miss occurs in the address
translation cache (ATC) of the memory management unit (MMU), or if the MMU finds a fault
with the access, the processor aborts the cycle before asserting AS. ECS can be used to
initiate various timing sequences that are eventually qualified with AS. Qualification with AS
may be required since, in the case of an internal cache hit, an ATC miss, or an MMU fault,
a bus cycle may be aborted after ECS has been asserted. The assertion of AS ensures that
the cycle has not been aborted by these internal conditions.
During the first external bus cycle of an operand transfer, the operand cycle start (OCS)
signal is asserted with ECS. When several bus cycles are required to transfer the entire
operand, OCS is asserted only at the beginning of the first external bus cycle. With respect
to OCS, an "operand'' is any entity required by the execution unit, whether a program or data
item.
The function code signals (FC0–FC2) are also driven at the beginning of a bus cycle. These
three signals select one of eight address spaces (refer to Table 4-1) to which the address
applies. Five address spaces are presently defined. Of the remaining three, one is reserved
Figure 7-2. Asynchronous Input Sample Window
tsu th
SAMPLE
WINDOW
CLK
EXT
Bus Operation
7-4
MC68030 USER’S MANUAL
MOTOROLA
for user definition and two are reserved by Motorola for future use. The function code signals
are valid while AS is asserted.
At the beginning of a bus cycle, the size signals (SIZ0 and SIZ1) are driven along with ECS
and the FC0–FC2. SIZ0 and SIZ1 indicate the number of bytes remaining to be transferred
during an operand cycle (consisting of one or more bus cycles) or during a cache fill
operation from a device with a port size that is less than 32 bits. Table 7-2 shows the
encoding of SIZ0 and SIZ1. These signals are valid while AS is asserted.
The read/write (R/W) signal determines the direction of the transfer during a bus cycle. This
signal changes state, when required, at the beginning of a bus cycle and is valid while AS
is asserted. R/W only transitions when a write cycle is preceded by a read cycle or vice
versa. The signal may remain low for two consecutive write cycles.
The read-modify-write cycle signal (RMC) is asserted at the beginning of the first bus cycle
of a read-modify-write operation and remains asserted until completion of the final bus cycle
of the operation. The RMC signal is guaranteed to be negated before the end of state 0 for
a bus cycle following a read-modify-write operation.
7.1.2 Address Bus
The address bus signals (A0–A31) define the address of the byte (or the most significant
byte) to be transferred during a bus cycle. The processor places the address on the bus at
the beginning of a bus cycle. The address is valid while AS is asserted.
7.1.3 Address Strobe
AS is a timing signal that indicates the validity of an address on the address bus and of many
control signals. It is asserted one-half clock after the beginning of a bus cycle.
Bus Operation
MOTOROLA
MC68030 USER’S MANUAL
7-5
7.1.4 Data Bus
The data bus signals (D0–D31) comprise a bidirectional, nonmultiplexed parallel bus that
contains the data being transferred to or from the processor. A read or write operation may
transfer 8, 16, 24, or 32 bits of data (one, two, three, or four bytes) in one bus cycle. During
a read cycle, the data is latched by the processor on the last falling edge of the clock for that
bus cycle. For a write cycle, all 32 bits of the data bus are driven, regardless of the port width
or operand size. The processor places the data on the data bus one-half clock cycle after
AS is asserted in a write cycle.
7.1.5 Data Strobe
The data strobe (DS) is a timing signal that applies to the data bus. For a read cycle, the
processor asserts DS to signal the external device to place data on the bus. It is asserted at
the same time as AS during a read cycle. For a write cycle, DS signals to the external device
that the data to be written is valid on the bus. The processor asserts DS one full clock cycle
after the assertion of AS during a write cycle.
7.1.6 Data Buffer Enable
The data buffer enable signal (DBEN) can be used to enable external data buffers while data
is present on the data bus. During a read operation, DBEN is asserted one clock cycle after
the beginning of the bus cycle and is negated as DS is negated. In a write operation, DBEN
is asserted at the time AS is asserted and is held active for the duration of the cycle. In a
synchronous system supporting two-clock bus cycles, DBEN timing may prevent its use.
7.1.7 Bus Cycle Termination Signals
During asynchronous bus cycles, external devices assert the data transfer and size
acknowledge signals (DSACK0 and/or DSACK1) as part of the bus protocol. During a read
cycle, the assertion of DSACKx signals the processor to terminate the bus cycle and to latch
the data. During a write cycle, the assertion of DSACKx indicates that the external device
has successfully stored the data and that the cycle may terminate. These signals also
indicate to the processor the size of the port for the bus cycle just completed, as shown in
Table 7-1. Refer to
7.3.1 Asynchronous Read Cycle
for timing relationships of DSACK0
and DSACK1.
Bus Operation
7-6
MC68030 USER’S MANUAL
MOTOROLA
For synchronous bus cycles, external devices assert the synchronous termination signal
(STERM) as part of the bus protocol. During a read cycle, the assertion of STERM causes
the processor to latch the data. During a write cycle, it indicates that the external device has
successfully stored the data. In either case, it terminates the cycle and indicates that the
transfer was made to a 32-bit port. Refer to
7.3.2 Asynchronous Write Cycle
for timing
relationships of STERM.
The bus error (BERR) signal is also a bus cycle termination indicator and can be used in the
absence of DSACKx or STERM to indicate a bus error condition. It can also be asserted in
conjunction with DSACKx or STERM to indicate a bus error condition, provided it meets the
appropriate timing described in this section and in MC68030EC/D,
MC68030 Electrical
Specifications
. Additionally, the BERR and HALT signals can be asserted together to
indicate a retry termination. Again, the BERR and HALT signals can be asserted
simultaneously in lieu of or in conjunction with the DSACKx or STERM signals.
Finally, the autovector (AVEC) signal can be used to terminate interrupt acknowledge
cycles, indicating that the MC68030 should internally generate a vector number to locate an
interrupt handler routine. AVEC is ignored during all other bus cycles.
7.2 DATA TRANSFER MECHANISM
The MC68030 architecture supports byte, word, and long-word operands allowing access
to 8-, 16-, and 32-bit data ports through the use of asynchronous cycles controlled by
DSACK0 and DSACK1. It also supports synchronous bus cycles to and from 32-bit ports,
terminated by STERM. Byte, word, and long-word operands can be located on any byte
boundary, but misaligned transfers may require additional bus cycles, regardless of port
size.
When the processor requests a burst mode fill operation, it asserts the cache burst request
(CBREQ) signal to attempt to fill four entries within a line in one of the on-chip caches. This
mode is compatible with nibble, static column, or page mode dynamic RAMs. The burst fill
operation uses synchronous bus cycles, each terminated by STERM, to fetch as many as
four long words.
7.2.1 Dynamic Bus Sizing
The MC68030 dynamically interprets the port size of the addressed device during each bus
cycle, allowing operand transfers to or from 8-, 16-, and 32-bit ports. During an
asynchronous operand transfer cycle, the slave device signals its port size (byte, word, or
long word) and indicates completion of the bus cycle to the processor through the use of the
DSACKx inputs. Refer to Table 7-1 for DSACKx encodings and assertion results.
Bus Operation
MOTOROLA
MC68030 USER’S MANUAL
7-7
For example, if the processor is executing an instruction that reads a long-word operand
from a long-word aligned address, it attempts to read 32 bits during the first bus cycle. (Refer
to
7.2.2 Misaligned Operands
for the case of a word or byte address.) If the port responds
that it is 32 bits wide, the MC68030 latches all 32 bits of data and continues with the next
operation. If the port responds that it is 16 bits wide, the MC68030 latches the 16 bits of valid
data and runs another bus cycle to obtain the other 16 bits. The operation for an 8-bit port
is similar, but requires four read cycles. The addressed device uses the DSACKx signals to
indicate the port width. For instance, a 32-bit device
always
returns DSACKx for a 32-bit port
(regardless of whether the bus cycle is a byte, word, or long-word operation).
Dynamic bus sizing requires that the portion of the data bus used for a transfer to or from a
particular port size be fixed. A 32-bit port must reside on data bus bits 0–31, a 16-bit port
must reside on data bus bits 16-32, and an 8-bit port must reside on data bus bits 24-31.
This requirement minimizes the number of bus cycles needed to transfer data to 8- and 16-
bit ports and ensures that the MC68030 correctly transfers valid data. The MC68030 always
attempts to transfer the maximum amount of data on all bus cycles; for a long-word
operation, it always assumes that the port is 32 bit wide when beginning the bus cycle.
The bytes of operands are designated as shown in Figure 7-3. The most significant byte of
a long-word operand is OP0, and OP3 is the least significant byte. The two bytes of a word-
length operand are OP2 (most significant) and OP3. The single byte of a byte-length
operand is OP3. These designations are used in the figures and descriptions that follow.
Table 7-1. DSACK Codes and Results
DSACK1 DSACK0
Result
H H Insert Wait States in Current Bus Cycle
H L Complete Cycle — Data Bus Port Size is 8 Bits
L H Complete Cycle — Data Bus Port Size is 16 Bits
L L Complete Cycle — Data Bus Port Size is 32 Bits
Bus Operation
7-8
MC68030 USER’S MANUAL
MOTOROLA
Figure 7-4 shows the required organization of data ports on the MC68030 bus for 8, 16, and
32-bit devices. The four bytes shown in Figure 7-4 are connected through the internal data
bus and data multiplexer to the external data bus. This path is the means through which the
MC68030 supports dynamic bus sizing and operand misalignment. Refer to
7.2.2
Misaligned Operands
for the definition of misaligned operand. The data multiplexer
establishes the necessary connections for different combinations of address and data sizes.
The multiplexer takes the four bytes of the 32-bit bus and routes them to their required
positions. For example, OP0 can be routed to D24–D31, as would be the normal case, or it
can be routed to any other byte position to support a misaligned transfer. The same is true
for any of the operand bytes. The positioning of bytes is determined by the size (SIZ0 and
SIZ1) and address (A0 and A1) outputs.
The SIZ0 and SIZ1 outputs indicate the remaining number of bytes to be transferred during
the current bus cycle, as shown in Table 7-2.
The number of bytes transferred during a write or noncachable read bus cycle is equal to or
less than the size indicated by the SIZ0 and SIZ1 outputs, depending on port width and
operand alignment. For example, during the first bus cycle of a long-word transfer to a word
port, the size outputs indicate that four bytes are to be transferred, although only two bytes
are moved on that bus cycle. Cachable read cycles must always transfer the number of
bytes indicated by the port size.
A0 and A1 also affect operation of the data multiplexer. During an operand transfer, A2–A31
indicate the long-word base address of that portion of the operand to be accessed; A0 and
A1 indicate the byte offset from the base. Table 7-3 shows the encodings of A0 and A1 and
the corresponding byte offsets from the long-word base.
Figure 7-3. Internal Operand Representation
OP0 OP1 OP2 OP3
31 0
15 0
OP2 OP3
70
LONG WORD OPERAND
WORD OPERAND
BYTE OPERAND OP3
Bus Operation
MOTOROLA
MC68030 USER’S MANUAL
7-9
Table 7-4 lists the bytes required on the data bus for read cycles that are cachable. The
entries shown as OPn are portions of the requested operand that are read or written during
that bus cycle and are defined by SIZ0, SIZ1, A0, and A1 for the bus cycle. The PRn and
the Nn bytes correspond to the previous and next bytes in memory, respectively, that must
be valid on the data bus for the specified port size (long word or word) so that the internal
caches operate correctly. (For cachable accesses, the MC68030 assumes that all portions
of the data bus for a given port size are valid.) This same table applies to noncachable read
cycles except that the bytes labeled PRn and Nn are not required and can be replaced by
“don't cares”.
Figure 7-4. MC68030 Interface to Various Port Sizes
Table 7-2. Size Signal
Encoding Table 7-3. Address Offset
Encodings
SIZ1 SIZ0 Size A1 A0 Offset
0 1 Byte 0 0 +0 Bytes
1 0 Word 0 1 +1 Byte
1 1 3 Bytes 1 0 +2 Bytes
0 0 Long Word 1 1 +3 Bytes
0123
ROUTING AND DUPLICATION
BYTE 0
BYTE 2
BYTE 1
BYTE 3 16-BIT PORT
REGISTER
MULTIPLEXER
EXTERNAL
DATA BUS
ADDRESS
xxxxxxxx0
xxxxxxxx0
2
INCREASING
MEMORY
ADDRESSES
D31- D24 D23-D16 D15-D8 D7-D0
BYTE 0 BYTE 1 BYTE 2 BYTE 3
BYTE 0
BYTE 1
BYTE 2
BYTE 3
8-BIT PORT
2
3
1
xxxxxxxx0
EXTERNAL BUS
INTERNAL TO
THE MC68EC030
32-BIT PORT
OP0 OP1 OP2 OP3
FIG 7
-
4
ab
Bus Operation
7-10
MC68030 USER’S MANUAL
MOTOROLA
Table 7-4. Data Bus Requirements for Read Cycles.
Table 7-5 lists the combinations of SIZ0, SIZ1, A0, and A1 and the corresponding pattern of
the data transfer for write cycles from the internal multiplexer of the MC68030 to the external
data bus.
Figure 7-5 shows the transfer of a long-word operand to a word port. In the first bus cycle,
the MC68030 places the four operand bytes on the external bus. Since the address is long-
word aligned in this example, the multiplexer follows the pattern in the entry of Table 7-5
corresponding to SIZ0_SIZ1_A0_A1=0000. The port latches the data on bits D16–D31 of
the data bus, asserts DSACK1 (DSACK0 remains negated), and the processor terminates
the bus cycle. It then starts a new bus cycle with SIZ0_SIZ1_A0_A1=1010 to transfer the
remaining 16 bits. SIZ0 and SIZ1 indicate that a word remains to be transferred; A0 and A1
indicate that the word corresponds to an offset of two from the base address. The
multiplexer follows the pattern corresponding to this configuration of the size and address
signals and places the two least significant bytes of the long word on the word portion of the
bus (D16–D31). The bus cycle transfers the remaining bytes to the word-size port. Figure 7-
6 shows the timing of the bus transfer signals for this operation.
(Table did not make it over in the conversion from Word)
Bus Operation
MOTOROLA
MC68030 USER’S MANUAL
7-11
Table 7-5. MC68030 Internal to External Data Bus.
(Table did not make it over in the conversion from Word)
Figure 7-5. Example of Long-Word Transfer to Word Port
DATA BUSD31 D16
LONG WORD OPERAND
OP0 OP1 OP2 OP3
31 0
WORD MEMORY
MSB LSB
OP0 OP1
OP2 OP3
MC68EC030
SIZ1 SIZ0 A1 A0
0000
1010
MEMORY CONTROL
DSACK1 DSACK0
LH
LH
Bus Operation
7-12
MC68030 USER’S MANUAL
MOTOROLA
Figure 7-7 shows a word transfer to an 8-bit bus port. Like the preceding example, this
example requires two bus cycles. Each bus cycle transfers a single byte. The size signals
for the first cycle specify two bytes; for the second cycle, one byte. Figure 7-8 shows the
associated bus transfer signal timing.
Figure 7-6. Long-Word Operand Write Timing (16-Bit Data Port)
WORD WRITE
LONG WORD OPERAND WRITE TO 16-BIT PORT
S0 S2 S4 S0 S2 S4
CLK
A31-A2
A1
A0
FC2-FC0
SIZ1
SIZ0
R/W
ECS
OCS
AS
DS
DSACK1
DSACK0
DBEN
D31-D24
D23-D16
WORD WRITE
OP0
OP1
OP2
OP3
Bus Operation
MOTOROLA
MC68030 USER’S MANUAL
7-13
7.2.2 Misaligned Operands
Since operands may reside at any byte boundaries, they may be misaligned. A byte
operand is properly aligned at any address; a word operand is misaligned at an odd address;
a long word is misaligned at an address that is not evenly divisible by four. The MC68000,
MC68008, and MC68010 implementations allow long-word transfers on odd-word
boundaries but force exceptions if word or long-word operand transfers are attempted at
odd-byte addresses. Although the MC68030 does not enforce any alignment restrictions for
data operands (including PC relative data addresses), some performance degradation
occurs when additional bus cycles are required for long-word or word operands that are
misaligned. For maximum performance, data items should be aligned on their natural
boundaries. All instruction words and extension words must reside on word boundaries.
Attempting to prefetch an instruction word at an odd address causes an address error
exception.
Figure 7-7. Example of Word Transfer to Byte Port
DATA BUSD31 D24
WORD OPERAND
OP2 OP3
15 0
BYTE MEMORY
OP2
OP3
MC68EC030
SIZ1 SIZ0 A1 A0
1000
0101
MEMORY CONTROL
DSACK1 DSACK0
LH LH
Bus Operation
7-14
MC68030 USER’S MANUAL
MOTOROLA
Figure 7-8. Word Operand Write Timing (8-Bit Data Port)
BYTE WRITE
WORD OPERAND WRITE
S0 S2 S4 S0 S2 S4
CLK
A31-A2
A1
A0
FC2-FC0
SIZ1
SIZ0
R/W
ECS
OCS
AS
DS
DSACK1
DSACK0
DBEN
D31-D24
D23-D16
BYTE WRITE
D15-D8
D7-D0 OP3
OP2
OP3
OP2
OP3
OP3
OP3
OP3
Bus Operation
MOTOROLA
MC68030 USER’S MANUAL
7-15
Figure 7-9 shows the transfer of a long-word operand to an odd address in word-organized
memory, which requires three bus cycles. For the first cycle, the size signals specify a long-
word transfer, and the address offset (A2:A0) is 001. Since the port width is 16 bits, only the
first byte of the long word is transferred. The slave device latches the byte and
acknowledges the data transfer, indicating that the port is 16 bits wide. When the processor
starts the second cycle, the size signals specify that three bytes remain to be transferred
with an address offset (A2:A0) of 010. The next two bytes are transferred during this cycle.
The processor then initiates the third cycle, with the size signals indicating one byte
remaining to be transferred. The address offset (A2:A0) is now 100; the port latches the final
byte; and the operation is complete. Figure 7-10 shows the associated bus transfer signal
timing.
Figure 7-11 shows the equivalent operation for a cachable data read cycle.
Figures 7-12 and 7-13 show a word transfer to an odd address in word-organized memory.
This example is similar to the one shown in Figures 7-9 and 7-10 except that the operand is
word sized and the transfer requires only two bus cycles.
Figure 7-14 shows the equivalent operation for a cachable data read cycle.
Figure 7-9. Misaligned Long-Word Transfer to Word Port Example
DATA BUS
D31 D16
LONG WORD OPERAND
OP0 OP1 OP2 OP3
31 0
WORD MEMORY
MSB LSB
XXX OP0
OP1 OP2
MC68EC030
SIZ1 SIZ0 A1 A0
0000
1101
MEMORY CONTROL
DSACK1 DSACK0
LH
LH
XXXOP3
LH
A0
1
0
01100
Bus Operation
7-16
MC68030 USER’S MANUAL
MOTOROLA
Figure 7-10. Misaligned Long-Word Transfer to Word Port
BYTE WRITE
LONG WORD OPERAND WRITE
S0 S2 S4 S0 S2 S4
CLK
A31-A2
A1
A0
FC2-FC0
SIZ1
SIZ0
R/W
ECS
OCS
AS
DS
DSACK1
DSACK0
DBEN
D31-D24
D23-D16
WORD WRITE
D15-D8
D7-D0
S0 S2 S4
OP0
OP0
OP1
OP2
OP1
OP2
OP1
OP2
OP3
OP3
OP3
OP3
BYTE WRITE
Bus Operation
MOTOROLA
MC68030 USER’S MANUAL
7-17
Figure 7-11. Misaligned Cachable Long-Word Transfer from Word Port Example
Figure 7-12. Misaligned Word Transfer to Word Port Example
LONG WORD OPERAND (REGISTER)
OP0 OP1 OP2 OP3
31 0
WORD MEMORY
MSB LSB
PR OP0
OP1 OP2
MC68EC030
SIZ1 SIZ0 A1 A0
0000
1101
MEMORY CONTROL
DSACK1 DSACK0
LH
LH
NOP3
LH
A0
1
0
0 1100
CACHE ENTRIES
PR OP0 OP1 OP2
31 0
OP3 N N1 N2
31 0
DATA BUS
D31 D16
N2N1
1 0110 L H
MC68030
SIZ1 SIZ0 A2 A1
1 0 0 0 1
0 1 0 1 0
A0
MEMORY CONTROL
DSACK1 DSACK0
LH
LH
OP2 OP3
15 0WORD OPERAND
DATA BUSD31 D16
WORD MEMORY
MSB LSB
XXX
OP3
OP2
XXX
Bus Operation
7-18
MC68030 USER’S MANUAL
MOTOROLA
Figure 7-13. Misaligned Word Transfer to Word Port
WORD OPERAND WRITE TO A1/A0=01
S0 S2 S4 S0 S2 S4
CLK
A31-A2
A1
A0
FC2-FC0
SIZ1
SIZ0
R/W
ECS
OCS
AS
DS
DSACK1
DSACK0
DBEN
D31-D24
D23-D16
WORD WRITE
D15-D8
D7-D0
OP2
OP2
OP3
OP2
OP3
OP3
OP3
OP3
BYTE WRITE
Bus Operation
MOTOROLA
MC68030 USER’S MANUAL
7-19
Figures 7-15 and 7-16 show an example of a long-word transfer to an odd address in long-
word-organized memory. In this example, a long-word access is attempted beginning at the
least significant byte of a long-word-organized memory. Only one byte can be transferred in
the first bus cycle. The second bus cycle then consists of a three-byte access to a long-word
boundary. Since the memory is long-word organized, no further bus cycles are necessary.
Figure 7-17 shows the equivalent operation for a cachable data read cycle.
7.2.3 Effects of Dynamic Bus Sizing and Operand Misalignment
The combination of operand size, operand alignment, and port size determines the number
of bus cycles required to perform a particular memory access. Table 7-6 shows the number
of bus cycles required for different operand sizes to different port sizes with all possible
alignment conditions for write cycles and noncachable read cycles.
Data Port Size — 32 Bits:16 Bits:8 Bits
*Instruction prefetches are always two words from a long-word boundary.
This table shows that bus cycle throughput is significantly affected by port size and
alignment. The MC68030 system designer and programmer should be aware of and
account for these effects, particularly in time-critical applications.
Table 7-6. Memory Alignment and Port Size Influence on Write Bus Cycles
A1/A0 Number of Bus Cycles
00 01 10 11
Instruction* 1:2:4 N/A N/A N/A
Byte Operand 1:1:1 1:1:1 1:1:1 1:1:1
Word Operand 1:1:2 1:2:2 1:1:2 2:2:2
Long-Word Operand 1:2:4 2:3:4 2:2:4 2:3:4
Bus Operation
7-20
MC68030 USER’S MANUAL
MOTOROLA
Table 7-6 shows that the processor always prefetches instructions by reading a long word
from a long-word address (A1:A0=00), regardless of port size or alignment. When the
required instruction begins at an odd-word boundary, the processor attempts to fetch the
entire 32 bits and loads both words into the instruction cache, if possible, although the
second one is the required word. Even if the instruction access is not cached, the entire 32
bits are latched into an internal cache holding register from which the two instructions words
can subsequently be referenced. Refer to
Section 11 Instruction Execution Timing
for a
complete description of the cache holding register and pipeline operation.
Figure 7-14. Example of Misaligned Cachable Word Transfer from Word Bus
Figure 7-15. Misaligned Long-Word Transfer to Long-Word Port
MC68EC030
SIZ1 SIZ0 A2 A1
1 0 0 0 1
0 1 0 1 0
A0
MEMORY CONTROL
DSACK1 DSACK0
LH
LH
OP2 OP3
15 0
WORD OPERAND (REGISTER)
DATA BUS
D31 D16
WORD MEMORY
MSB LSB
XXX
OP3
OP2
XXX
PR OP2
31 0CACHE ENTRY
OP3 N
MC68EC030
SIZ1 SIZ0 A2 A1
0 0 0 1 1
1 1 1 0 0
A0
MEMORY CONTROL
DSACK1 DSACK0
L
LL
OP0 OP1
15 0LONG WORD OPERAND
DATA BUSD31 D0
LONG WORD MEMORY
MSB UMB
XXX
OP1 OP2
XXX XXX
OP2 OP3
OP3
OP0
XXX
LMB LSB
L
Bus Operation
MOTOROLA
MC68030 USER’S MANUAL
7-21
Figure 7-16. Misaligned Write Cycles to Long-Word Port
LONG WORD OPERAND WRITE
S0 S2 S4 S0 S2 S4
CLK
A31-A2
A1
A0
FC2-FC0
SIZ1
SIZ0
R/W
ECS
OCS
AS
DS
DSACK1
DSACK0
DBEN
D31-D24
D23-D16
BYTE WRITE
D15-D8
D7-D0
OP0
OP0
OP1
OP0
OP1
OP2
OP3
OP1
3 - BYTE WRITE
Bus Operation
7-22
MC68030 USER’S MANUAL
MOTOROLA
7.2.4 Address, Size, and Data Bus Relationships
The data transfer examples show how the MC68030 drives data onto or receives data from
the correct byte sections of the data bus. Table 7-7 shows the combinations of the size
signals and address signals that are used to generate byte enable signals for each of the
four sections of the data bus for noncachable read cycles and all write cycles if the
addressed device requires them. The port size also affects the generation of these enable
signals as shown in the table. The four columns on the right correspond to the four byte
enable signals. Letters B, W, and L refer to port sizes: B for 8-bit ports, W for 16-bit ports,
and L for 32-bit ports. The letters B, W, and L imply that the byte enable signal should be
true for that port size. A dash (—) implies that the byte enable signal does not apply.
The MC68030 always drives all sections of the data bus because, at the start of a write
cycle, the bus controller does not know the port size. The byte enable signals in the table
apply only to read operations that are not to be internally cached and to write operations.
For cachable read cycles, during which the data is cached, the addressed port must drive
all sections of the bus on which it resides.
Figure 7-17. Misaligned Cachable Long-Word Transfer from Long-Word Bus
MC68EC030
SIZ1 SIZ0 A2 A1
0 0 0 1 1
1 1 1 0 0
A0
MEMORY CONTROL
DSACK1 DSACK0
L
LL
OP0 OP1
31 0LONG WORD OPERAND (REGISTER)
DATA BUS
D31 D0
LONG WORD MEMORY
MSB UMB
PR2
OP1 OP2
PR1
OP2 OP3
PR
OP3
OP0
N
LMB LSB
L
PR2 PR1
31 0CACHE ENTRIES
PR OP0
OP1 OP2
31 0
OP3 N
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-23
The table shows that the MC68030 transfers the number of bytes specified by the size
signals to or from the specified address unless the operand is misaligned or the number of
bytes is greater than the port width. In these cases, the device transfers the greatest number
of bytes possible for the port. For example, if the size is four bytes and the address offset
(A1:A0) is 01, a 32-bit slave can only receive three bytes in the current bus cycle. A 16- or
8-bit[lz slave can only receive one byte. The table defines the byte enables for all port sizes.
Byte data strobes can be obtained by combining the enable signals with the data strobe
signal. Devices residing on 8-bit ports can use the data strobe by itself since there is only
one valid byte for every transfer. These enable or strobe signals select only the bytes
required for write cycles or for noncachable read cycles. The other bytes are not selected,
which prevents incorrect accesses in sensitive areas such as I/O.
Figure 7-18 shows a logic diagram for one method for generating byte data enable signals
for 16- and 32-bit ports from the size and address encodings and the read/write signal.
Table 7-7. Data Bus Write Enable Signals for
Byte, Word, and Long-Word Ports
Transfer
Size SIZ1 SIZ0 A1 A0 Data Bus Active Sections
Byte (B) - Word (W) - Long-Word (L) Ports
D31:D24 D23:D16 D15:D8 D7:D0
Byte 0
0
0
0
1
1
1
1
0
0
1
1
0
1
0
1
BWL
B
BW
B
—
WL
—
W
—
—
L
—
—
—
—
L
Word 1
1
1
1
0
0
0
0
0
0
1
1
0
1
0
1
BWL
B
BW
B
WL
WL
W
W
—
L
L
—
—
—
L
L
3 Byte 1
1
1
1
1
1
1
1
0
0
1
1
0
1
0
1
BWL
B
BW
B
WL
WL
W
W
L
L
L
—
—
L
L
L
Long Word 0
0
0
0
0
0
0
0
0
0
1
1
0
1
0
1
BWL
B
BW
B
WL
WL
W
W
L
L
L
—
L
L
L
L
Bus Operation
7-24 MC68030 USER’S MANUAL MOTOROLA
7.2.5 MC68030 versus MC68020 Dynamic Bus Sizing
The MC68030 supports the dynamic bus sizing mechanism of the MC68020 for
asynchronous bus cycles (terminated with DSACKx) with two restrictions. First, for a
cachable access within the boundaries of an aligned long word, the port size must be
consistent throughout the transfer of each long word. For example, when a byte port resides
at address $00, addresses $01, $02, and $03 must also correspond to byte ports. Second,
the port must supply as much data as it signals as port size, regardless of the transfer size
indicated with the size signals and the address offset indicated by A0 and A1 for cachable
accesses. Otherwise, dynamic bus sizing is identical in the two processors.
7.2.6 Cache Filling
The on-chip data and instruction caches, described in Section 6 On-Chip Cache
Memories, are each organized as 16 lines of four long-word entries each. For each line, a
tag contains the most significant bits of the logical address, FC2 (instruction cache) or FC0–
FC2 (data cache), and a valid bit for each entry in the line. An entry fill operation loads an
entire long word accessed from memory into a cache entry. This type of fill operation is
performed when one entry of a line is not valid and an access is cachable. A burst fill
operation is requested when a tag miss occurs for the current cycle or when all four entires
in the cache line are invalid (provided the cache is enabled and burst filling for the cache is
enabled). The burst fill operation attempts to fill all four entries in the line. To support burst
filling, the slave device must have a 32-bit port and must have a burst mode capability; that
is, it must acknowledge a burst request with the cache burst acknowledge (CBACK) signal.
It must also terminate the burst accesses with STERM and place a long word on the data
bus for each transfer. The device may continue to supply successive long words, asserting
STERM with each one, until the cache line is full. For further information about filling the
cache, both entry fills and burst mode fills, refer to 6.1.3 Cache Filling, 7.3.4 Synchronous
Read Cycle, 7.3.5 Synchronous Write Cycle, and 7.3.7 Burst Operation Cycles, which
discuss in detail the required bus cycles.
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-25
7.2.7 Cache Interactions
The organization and requirements of the on-chip instruction and data caches affect the
interpretation of the DSACKx and STERM signals. Since the MC68030 attempts to load all
data operands and instructions that are cachable into the on-chip caches, the bus may
operate differently when caching is enabled. Specifically, on cachable read cycles that
terminate normally, the low-order address signals (A0 and A1) and the size signals do not
apply.
The slave device must supply as much aligned data on the data bus as its port size allows,
regardless of the requested operand size. This means that an 8-bit port must supply a byte,
a 16-bit port must supply a word, and a 32-bit port must supply an entire long word. This
data is loaded into the cache. For a 32-bit port, the slave device ignores A0 and A1 and
supplies the long word beginning at the long-word boundary on the data bus. For a 16-bit[lz
port, the device ignores A0 and supplies the entire word beginning at the lower word
boundary on D16–D31 of the data bus. For a byte port, the device supplies the addressed
byte on D24–D31.
If the addressed device cannot supply port-sized data or if the data should not be cached,
the device must assert cache inhibit in (CIIN) as it terminates the read cycle. If the bus cycle
terminates abnormally, the MC68030 does not cache the data. For details of interactions of
port sizes, misalignments, and cache filling, refer to 6.1.3 Cache Filling.
The caches can also affect the assertion of AS and the operation of a read cycle. The search
of the appropriate cache by the processor begins when the microsequencer requires an
instruction or a data item. At this time, the bus controller may also initiate an external bus
cycle in case the requested item is not resident in the instruction or data cache. If the bus is
not occupied with another read or write cycle, the bus controller asserts the ECS signal (and
the OCS signal, if appropriate). If an internal cache hit occurs, the external cycle aborts, and
AS is not asserted. This makes it possible to have ECS asserted on multiple consecutive
clock cycles. Notice that there is a minimum time specified from the negation of ECS to the
next assertion of ECS (refer to MC68030EC/D,
MC68030 Electrical Specifications
.
Instruction prefetches can occur every other clock so that if, after an aborted cycle due to an
instruction cache hit, the bus controller asserts ECS on the next clock, this second cycle is
for a data fetch. However, data accesses that hit in the data cache can also cause the
assertion of ECS and an aborted cycle. Therefore, since instruction and data accesses are
mixed, it is possible to see multiple successive ECS assertions on the external bus if the
processor is hitting in both caches and if the bus controller is free. Note that, if the bus
controller is executing other cycles, these aborted cycles due to cache hits may not be seen
externally. Also, OCS is asserted for the first external cycle of an operand transfer.
Therefore, in the case of a misaligned data transfer where the first portion of the operand
results in a cache hit (but the bus controller did not begin an external cycle and then abort
it) and the second portion in a cache miss, OCS is asserted for the second portion of the
operand.
Bus Operation
7-26 MC68030 USER’S MANUAL MOTOROLA
Figure 7-18. Byte Data Select Generation for 16- and 32-Bit Ports
A1
SIZ0
SIZ1
R/W
LD
UD
LLD
LMD
UMD
UUD
UUD = UPPER UPPER DATA (32-BIT PORT)
UMD = UPPER MIDDLE DATA (32-BIT PORT)
LMD = LOWER MIDDLE DATA (32-BIT PORT)
LLD = LOWER LOWER DATA (32-BIT PORT)
UD = UPPER DATA (16-BIT PORT)
LD = LOWER DATA (16-BIT PORT)
NOTE: These select lines can be combined with the address decode circuitry or all can be generated within the same
programmed array logic unit.
A0
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-27
7.2.8 Asynchronous Operation
The MC68030 bus may be used in an asynchonous manner. In that case, the external
devices connected to the bus can operate at clock frequencies different from the clock for
the MC68030. Asynchronous operation requires using only the handshake line (AS, DS,
DSACK1, DSACK0, BERR, and HALT) to control data transfers. Using this method, AS
signals the start of a bus cycle, and DS is used as a condition for valid data on a write cycle.
Decoding the size outputs and lower address lines (A0 and A1) provides strobes that select
the active portion of the data bus. The slave device (memory or peripheral) then responds
by placing the requested data on the correct portion of the data bus for a read cycle or
latching the data on a write cycle, and asserting the DSACK1/DSACK0 combination that
corresponds to the port size to terminate the cycle. If no slave responds or the access is
invalid, external control logic asserts the BERR or BERR and HALT signal(s) to abort or retry
the bus cycle, respectively.
The DSACKx signals can be asserted before the data from a slave device is valid on a read
cycle. The length of time that DSACKx may precede data is given by parameter #31, and it
must be met in any asynchronous system to insure that valid data is latched into the
processor. (Refer to MC68030EC/D,
MC68030 Electrical Specifications
for timing
parameters.) Notice that no maximum time is specified from the assertion of AS to the
assertion of DSACKx. Although the processor can transfer data in a minimum of three clock
cycles when the cycle is terminated with DSACKx, the processor inserts wait cycles in clock
period increments until DSACKx is recognized.
The BERR and/or HALT signals can be asserted after the DSACKx signal(s) is asserted.
BERR and/or HALT must be asserted within the time given as parameter #48, after DSACKx
is asserted in any asynchronous system. If this maximum delay time is violated, the
processor may exhibit erratic behavior.
Bus Operation
7-28 MC68030 USER’S MANUAL MOTOROLA
For asynchronous read cycles, the value of CIIN is internally latched on the rising edge of
bus cycle state 4. Refer to 7.3.1 Asynchronous Read Cycle for more details on the states
for asynchonous read cycles.
During any bus cycle terminated by DSACKx or BERR, the assertion of CBACK is
completely ignored.
7.2.9 Synchronous Operation with DSACKx
Although cycles terminated with the DSACKx signals are classified as asynchronous and
cycles terminated with STERM are classified as synchronous, cycles terminated with
DSACKx can also operate synchronously in that signals are interpreted relative to clock
edges.
The devices that use these cycles must synchronize the responses to the MC68030 clock
to be synchronous. Since they terminate bus cycles with the DSACKx signals, the dynamic
bus sizing capabilities of the MC68030 are available. In addition, the minimum cycle time for
these cycles is also three clocks.
To support those systems that use the system clock to generate DSACKx and other
asynchronous inputs, the asynchronous input setup time (parameter #47A) and the
asynchronous input hold time (parameter #47B) are given. If the setup and hold times are
met for the assertion or negation of a signal, such as DSACKx, the processor can be
guaranteed to recognize that signal level on that specific falling edge of the system clock. If
the assertion of DSACKx is recognized on a particular falling edge of the clock, valid data is
latched into the processor (for a read cycle) on the next falling clock edge provided the data
meets the data setup time (parameter #27). In this case, parameter #31 for asynchronous
operation can be ignored. The timing parameters referred to are described in MC68030EC/
D,
MC68030 Electrical Specifications
. If a system asserts DSACKx for the required window
around the falling edge of S2 and obeys the proper bus protocol by maintaining DSACKx
(and/or BERR/HALT) until and throughout the clock edge that negates AS (with the
appropriate asynchronous input hold time specified by parameter #47B), no wait states are
inserted. The bus cycle runs at its maximum speed (three clocks per cycle) for bus cycles
terminated with DSACKx.
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-29
To assure proper operation in a synchronous system when BERR or BERR and HALT is
asserted after DSACKx, BERR (and HALT) must meet the appropriate setup time
(parameter #27A) prior to the falling clock edge one clock cycle after DSACKx is recognized.
This setup time is critical, and the MC68030 may exhibit erratic behavior if it is violated.
When operating synchronously, the data-in setup and hold times for synchronous cycles
may be used instead of the timing requirements for data relative to the DS signal.
The value of CIIN is latched on the rising edge of bus cycle state 4 for all cycles terminated
with DSACKx.
7.2.10 Synchronous Operation with STERM
The MC68030 supports synchronous bus cycles terminated with STERM. These cycles, for
32-bit ports only, are similar to cycles terminated with DSACKx. The main difference is that
STERM can be asserted (and data can be transferred) earlier than for a cycle terminated
with DSACKx, causing the processor to perform a minimum access time transfer in two
clock periods. However, wait cycles can be inserted by delaying the assertion of STERM
appropriately.
Using STERM instead of DSACKx in any bus cycle makes the cycle synchronous. Any bus
cycle is synchronous if:
1. Neither DSACKx nor AVEC is recognized during the cycle.
2. The port size is 32 bits.
3. Synchronous input setup and hold time requirements (specifications #60 and #61) for
STERM are met.
Burst mode operation requires the use of STERM to terminate each of its cycles. The first
cycle of any burst transfer must be a synchronous cycle as described in the preceding
paragraph. The exact timing of this cycle is controlled by the assertion of STERM, and wait
cycles can be inserted as necessary. However, the minimum cycle time is two clocks. If a
burst operation is initiated and allowed to terminate normally, the second, third, and fourth
cycles latch data on successive falling edges of the clock at a minimum. Again, the exact
timing for these subsequent cycles is controlled by the timing of STERM for each of these
cycles, and wait cycles can be inserted as necessary.
Bus Operation
7-30 MC68030 USER’S MANUAL MOTOROLA
Although the synchronous input signals (STERM, CIIN, and CBACK) must be stable for the
appropriate setup and hold times relative to every rising edge of the clock during which AS
is asserted, the assertion or negation of CBACK and CIIN is internally latched on the rising
edge of the clock for which STERM is asserted in a synchronous cycle.
The STERM signal can be generated from the address bus and function code value and
does not need to be qualified with the AS signal. If STERM is asserted and no cycle is in
progress (even if the cycle has begun, ECS is asserted and then the cycle is aborted),
STERM is ignored by the MC68030.
Similarly, CBACK can be asserted independently of the assertion of CBREQ. If a cache
burst is not requested, the assertion of CBACK is ignored.
The assertion of CIIN is ignored when the appropriate cache is not enabled or when cache
inhibit out (CIOUT) is asserted. It is also ignored during write cycles or translation table
searches.
NOTE
STERM and DSACKx should never be asserted during the same
bus cycle.
7.3 DATA TRANSFER CYCLES
The transfer of data between the processor and other devices involves the following signals:
• Address Bus A0–A31
• Data Bus D0–D31
• Control Signals
The address and data buses are both parallel nonmultiplexed buses. The bus master moves
data on the bus by issuing control signals, and the asynchronous/synchronous bus uses a
handshake protocol to insure correct movement of the data. In all bus cycles, the bus master
is responsible for de-skewing all signals it issues at both the start and the end of the cycle.
In addition, the bus master is responsible for de-skewing the acknowledge and data signals
from the slave devices. The following paragraphs define read, write, and read-modify-write
cycle operations. An additional paragraph describes burst mode transfers.
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-31
Each of the bus cycles is defined as a succession of states. These states apply to the bus
operation and are different from the processor states described in Section 4 Processing
States. The clock cycles used in the descriptions and timing diagrams of data transfer
cycles are independent of the clock frequency. Bus operations are described in terms of
external bus states.
7.3.1 Asynchronous Read Cycle
During a read cycle, the processor receives data from a memory, coprocessor, or peripheral
device. If the instruction specifies a long-word operation, the MC68030 attempts to read four
bytes at once. For a word operation, it attempts to read two bytes at once, and for a byte
operation, one byte. For some operations, the processor requests a three-byte transfer. The
processor properly positions each byte internally. The section of the data bus from which
each byte is read depends on the operand size, address signals (A0–A1), CIIN and CIOUT,
whether the internal caches are enabled, and the port size. Refer to 7.2.1 Dynamic Bus
Sizing, 7.2.2 Misaligned Operands, and 7.2.6 Cache Filling for more information on
dynamic bus sizing, misaligned operands, and cache interactions.
Figure 7-19 is a flowchart of an asynchronous long-word read cycle. Figure 7-20 is a
flowchart of a byte read cycle. The following figures show functional read cycle timing
diagrams specified in terms of clock periods. Figure 7-21 corresponds to byte and word read
cycles from a 32-bit port. Figure 7-22 corresponds to a long-word read cycle from an 8-bit
port. Figure 7-23 also applies to a long-word read cycle, but from a 16-bit port.
State 0
The read cycle starts in state 0 (S0). The processor drives ECS low, indicating the
beginning of an external cycle. When the cycle is the first external cycle of a read operand
operation, operand cycle start (OCS) is driven low at the same time. During S0, the
processor places a valid address on A0–A31 and valid function codes on FC0–FC2. The
function codes select the address space for the cycle. The processor drives R/W high for
a read cycle and drives DBEN inactive to disable the data buffers. SIZ0–SIZ1 become
valid, indicating the number of bytes requested to be transferred. CIOUT also becomes
valid, indicating the state of the MMU CI bit in the address translation descriptor or in the
appropriate TTx register.
Bus Operation
7-32 MC68030 USER’S MANUAL MOTOROLA
Figure 7-19. Asynchronous Long-Word Read Cycle Flowchart
Figure 7-20. Asynchronous Byte Read Cycle Flowchart
CONTROLLER
ADDRESS DEVICE
1) ASSERT ECS/OCS FOR ONE-HALF CLOCK
2) SET R/W TO READ
3) DRIVE ADDRESS ON A31-A0
4) DRIVE FUNCTION CODE ON FC2-FC0
5) DRIVE SIZE (SIZ1-SIZ0) (FOUR BYTES)
6) CACHE INHIBIT OUT (CIOUT) BECOMES VALID
7) ASSERT ADDRESS STROBE (AS)
8) ASSERT DATA STROBE (DS)
9) ASSERT DATA BUFFER ENABLE (DBEN)
ACQUIRE DATA
2) LATCH DATA
3) NEGATE AS AND DS
4) NEGATE DBEN
START NEXT CYCLE
PRESENT DATA
1) DECODE ADDRESS
2) PLACE DATA ON D31-D0
3) ASSERT DATA TRANSFER AND SIZE
ACKNOWLEDGE (DSACKx)
TERMINATE CYCLE
1) REMOVE DATA FROM D31-D0
2) NEGATE DSACK
EXTERNAL DEVICE
1) SAMPLE CACHE IN (CIN)
START NEXT CYCLE
PRESENT DATA
1) DECODE ADDRESS
2) PLACE DATA ON D31-D324 OR
D23-D16 OR
D15-D8 OR
D7-D0
(BASED ON A1,A0, CACHE AND BUS WIDTH)
3) ASSERT DATA TRANSFER AND SIZE
ACKNOWLEDGE (DSACKx)
TERMINATE CYCLE
1) REMOVE DATA FROM D31-D0
2) NEGATE DSACK
EXTERNAL DEVICECONTROLLER
ADDRESS DEVICE
1) ASSERT ECS/OCS FOR ONE-HALF CLOCK
2) SET R/W TO READ
3) DRIVE ADDRESS ON A31-A0
4) DRIVE FUNCTION CODE ON FC2-FC0
5) DRIVE SIZE (SIZ1-SIZ0) (FOUR BYTES)
6) CACHE INHIBIT OUT (CIOUT) BECOMES VALID
7) ASSERT ADDRESS STROBE (AS)
8) ASSERT DATA STROBE (DS)
9) ASSERT DATA BUFFER ENABLE (DBEN)
ACQUIRE DATA
2) LATCH DATA
3) NEGATE AS AND DS
4) NEGATE DBEN
1)SAMPLE CACHE INHIBIT IN (CIIN)
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-33
Figure 7-21. Asynchronous Byte and Word Read Cycles — 32-Bit Port
WORD READ
S0 S2 S4 S0 S2 S4
BYTE READ
CLK
A31-A2
A1
A0
FC2-FC0
SIZ1
SIZ0
R/W
ECS
OCS
AS
DS
DSACK1
DSACK0
DBEN
D31-D24
D23-D16
D15-D8
D7-D0
S0 S2 S4
OP2
OP3
OP3
OP3
BYTEWORD
BYTE READ
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-35
Figure 7-22. Long-Word Read — 8-Bit Port with CIOUT Asserted
CLK
A31-A2
A1
A0
FC2-FC0
SIZ1
SIZ0
R/W
ECS
OCS
AS
DS
DSACK1
CIOUT
DSACK0
DBEN
D31-D24
D23-D16
D15-D8
D7-D0
BYTE READ
OP0 OP1 OP3
LONG WORD 3-BYTE
BYTE READ
WORD BYTE
OP2
BYTE READBYTE READ
LONG WORD OPERAND READ FROM 8-BIT PORT
S0 S2 S4 S0 S2 S4 S0 S2 S4 S0 S2 S4
Bus Operation
7-36 MC68030 USER’S MANUAL MOTOROLA
Figure 7-23. Long-Word Read — 16-Bit and 32-Bit Port
CLK
A31-A2
A1
A0
FC2-FC0
SIZ1
SIZ0
R/W
ECS
OCS
AS
DS
DSACK1
DSACK0
DBEN
D31-D24
D23-D16
D15-D8
D7-D0
WORD READ
S0 S2 S4 S0 S2 S4
WORD READ
S0 S2 S4
OP0
OP1 OP3
OP3
LONG WORD WORD
LONG WORD READ
FROM 32- BIT PORT
OP2
OP1
OP0
OP2
LONG WORD
LONG WORD OPERAND READ FROM 16-BIT PORT
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-37
State 1
One-half clock later in state 1 (S1), the processor asserts AS indicating that the address
on the address bus is valid. The processor also asserts DS also during S1. In addition,
the ECS (and OCS, if asserted) signal is negated during S1.
State 2
During state 2 (S2), the processor asserts DBEN to enable external data buffers. The
selected device uses R/W, SIZ0–SIZ1, A0–A1, CIOUT, and DS to place its information on
the data bus, and drives CIIN if appropriate. Any or all of the bytes (D24–D31, D16–D23,
D8–D15, and D0–D7) are selected by SIZ0–SIZ1 and A0–A1. Concurrently, the selected
device asserts DSACKx.
State 3
As long as at least one of the DSACKx signals is recognized by the end of S2 (meeting
the asynchronous input setup time requirement), data is latched on the next falling edge
of the clock, and the cycle terminates. If DSACKx is not recognized by the start of state 3
(S3), the processor inserts wait states instead of proceeding to states 4 and 5. To ensure
that wait states are inserted, both DSACK0 and DSACK1 must remain negated
throughout the asynchronous input setup and hold times around the end of S2. If wait
states are added, the processor continues to sample the DSACKx signals on the falling
edges of the clock until one is recognized.
State 4
The processor samples CIIN at the beginning of state 4 (S4). Since CIIN is defined as a
synchronous input, whether asserted or negated, it must meet the appropriate
synchronous input setup and hold times on every rising edge of the clock while AS is
asserted. At the end of S4, the processor latches the incoming data.
State 5
The processor negates AS, DS, and DBEN during state 5 (S5). It holds the address valid
during S5 to provide address hold time for memory systems. R/W, SIZ0–SIZ1, and FC0–
FC2 also remain valid throughout S5.
The external device keeps its data and DSACKx signals asserted until it detects the
negation of AS or DS (whichever it detects first). The device must remove its data and
negate DSACKx within approximately one clock period after sensing the negation of AS
or DS. DSACKx signals that remain asserted beyond this limit may be prematurely
detected for the next bus cycle.
Bus Operation
7-38 MC68030 USER’S MANUAL MOTOROLA
7.3.2 Asynchronous Write Cycle
During a write cycle, the processor transfers data to memory or a peripheral device.
Figure 7-24 is a flowchart of a write cycle operation for a long-word transfer. The following
figures show the functional write cycle timing diagrams specified in terms of clock periods.
Figure 7-25 shows two write cycles (between two read cycles with no idle time) for a 32-bit
port. Figure 7-26 shows byte and word write cycles to a 32-bit port. Figure 7-27 shows a
long-word write cycle to an 8-bit port. Figure 7-28 shows a long-word write cycle to a 16-bit
port.
Figure 7-24. Asynchronous Write Cycle Flowchart
1) ASSERT ECS/OCS FOR ONE-HALF CLOCK
2) DRIVE ADDRESS ON A31-A0
3) DRIVE FUNCTION CODE ON FC2-FC0
4) DRIVE SIZE (SIZ1-SIZ0) (FOUR BYTES)
5) SET R/W TO WRITE
6) CACHE INHIBIT OUT (CIOUT) BECOMES VALID
7) ASSERT ADDRESS STROBE (AS)
8) ASSERT DATA BUFFER ENABLE (DBEN)
9) DRIVE DATA LINES D31-D0
10) ASSERT DATA STROBE (DS)
1) NEGATE AS AND DS
2) REMOVE DATA FROM D31-D0
3) NEGATE DBEN
EXTERNAL DEVICECONTROLLER
1) NEGATE DSACKx
TERMINATE CYCLE
ACCEPT DATA
1) DECODE ADDRSS
2) STORE DATA FROM D31-D0
3) ASSERT DATA TRANSFER AND SIZE
ACKNOWLEDGE (DSACKx)
ADDRESS DEVICE
TERMINATE OUTPUT TRANSFER
START NEXT CYCLE
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-39
State 0
The write cycle starts in S0. The processor drives ECS low, indicating the beginning of
an external cycle. When the cycle is the first external cycle of a write operation, OCS is
driven low at the same time. During S0, the processor places a valid address on A0–A31
and valid function codes on FC0–FC2. The function codes select the address space for
the cycle. The processor drives R/W low for a write cycle. SIZ0–SIZ1 become valid,
indicating the number of bytes to be transferred. CIOUT also becomes valid, indicating
Figure 7-25. Asynchronous Read-Write-Read Cycles — 32-Bit Port
CLK
A31-A2
A1
A0
FC2-FC0
SIZ1
SIZ0
R/W
ECS
OCS
AS
DS
DSACK1
DSACK0
DBEN
D31-D0
WRITE
LONG WORD
WRITE
READ
S0 S2 S4 S0 S2 S4 S0 S2 S4 S0 S2 Sw Sw S4
READ WITH WAIT STATES
Bus Operation
7-40 MC68030 USER’S MANUAL MOTOROLA
the state of the MMU CI bit in the address translation descriptor or in the appropriate TTx
register.
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-41
Figure 7-26. Asynchronous Byte and Word Write Cycles — 32-Bit Port
CLK
A31-A2
A1
A0
FC2-FC0
SIZ1
SIZ0
R/W
ECS
OCS
AS
DS
DSACK1
DSACK0
DBEN
D31-D24
D23-D16
D15-D8
D7-D0
WORD WRITE
S0 S2 S4 S0 S4
BYTE WRITE
S0 S2S2 S4
OP2
OP3 OP3
OP3
WORD
OP3
OP3
OP3
OP3
BYTE
OP2
OP3 OP3
OP3
BYTE WRITE
Bus Operation
7-42 MC68030 USER’S MANUAL MOTOROLA
Figure 7-27. Long-Word Operand Write — 8-Bit Port
CLK
A31-A2
A1
A0
FC2-FC0
SIZ1
SIZ0
R/W
ECS
OCS
AS
DS
DSACK1
DSACK0
DBEN
D31-D24
D23-D16
D15-D8
D7-D0
BYTE WRITE
LONG WORD 3-BYTE
BYTE WRITE
WORD BYTE
BYTE WRITEBYTE WRITE
LONG WORD OPERAND READ TO 8-BIT PORT
S0 S2 S2S4 S0 S4 S0 S2 S4 S0 S2 S4
OP0 OP3
OP2
OP1
OP1 OP3OP3
OP1
OP2 OP3
OP2
OP2
OP3 OP3OP3OP3
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-43
Figure 7-28. Long-Word Operand Write — 16-Bit Port
CLK
A31-A2
A1
A0
FC2-FC0
SIZ1
SIZ0
R/W
ECS
OCS
AS
DS
DSACK1
DSACK0
DBEN
D31-D24
D23-D16
D15-D8
D7-D0
WORD WRITE
S0 S2 S2S4 S0 S4
WORD WRITE
S0 S2 S4
OP0
OP1 OP3
OP3
LONG WORD
OP2
OP1
OP0OP2
WORD
OP2
OP3 OP3
OP2
LONG WORD WRITE
TO 32-BIT PORT
LONG WORD OPERAND WRITE TO 16-BIT PORT
LONG WORD
Bus Operation
7-44 MC68030 USER’S MANUAL MOTOROLA
State 1
One-half clock later in S1, the processor asserts AS, indicating that the address on the
address bus is valid. The processor also asserts DBEN during S1, which can enable
external data buffers. In addition, the ECS (and OCS, if asserted) signal is negated during
S1.
State 2
During S2, the processor places the data to be written onto the D0–D31, and samples
DSACKx at the end of S2.
State 3
The processor asserts DS during S3, indicating that the data is stable on the data bus. As
long as at least one of the DSACKx signals is recognized by the end of S2 meeting the
asynchronous input setup time requirement), the cycle terminates one clock later. If
DSACKx is not recognized by the start of S3, the processor inserts wait states instead of
proceeding to S4 and S5. To ensure that wait states are inserted, both DSACK0 and
DSACK1 must remain negated throughout the asynchronous input setup and hold times
around the end of S2. If wait states are added, the processor continues to sample the
DSACKx signals on the falling edges of the clock until one is recognized. The selected
device uses R/W, DS, SIZ0–SIZ1, and A0–A1 to latch data from the appropriate byte(s)
of the data bus (D24–D31, D16–D23, D8–D15, and D0–D7). SIZ0–SIZ1 and A0–A1
select the bytes of the data bus. If it has not already done so, the device asserts DSACKx
to signal that it has successfully stored the data.
State 4
The processor issues no new control signals during S4.
State 5
The processor negates AS and DS during S5. It holds the address and data valid during
S5 to provide address hold time for memory systems. R/W, SIZ0–SIZ1, FC0–FC2, and
DBEN also remain valid throughout S5.
The external device must keep DSACKx asserted until it detects the negation of AS or
DS (whichever it detects first). The device must negate DSACKx within approximately
one clock period after sensing the negation of AS or DS. DSACKx signals that remain
asserted beyond this limit may be prematurely detected for the next bus cycle.
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-45
7.3.3 Asynchronous Read-Modify-Write Cycle
The read-modify-write cycle performs a read, conditionally modifies the data in the
arithmetic logic unit, and may write the data out to memory. In the MC68030 processor, this
operation is indivisible, providing semaphore capabilities for multiprocessor systems. During
the entire read-modify-write sequence, the MC68030 asserts the RMC signal to indicate that
an indivisible operation is occurring. The MC68030 does not issue a bus grant (BG) signal
in response to a bus request (BR) signal during this operation. The read portion of a read-
modify-write operation is forced to miss in the data cache because the data in the cache
would not be valid if another processor had altered the value being read. However, read-
modify-write cycles may alter the contents of the data cache as described in 6.1.2 Data
Cache.
No burst filling of the data cache occurs during a read-modify-write operation.
The test and set (TAS) and compare and swap (CAS and CAS2) instructions are the only
MC68030 instructions that utilize read-modify-write operations. Depending on the compare
results of the CAS and CAS2 instructions, the write cycle(s) may not occur. Table search
accesses required for the MMU are always read-modify-write cycles to the supervisor data
space. During these cycles, a write does not occur unless a descriptor is updated. No data
is internally cached for table search accesses since the MMU uses physical addresses to
access the tables. Refer to Section 9 Memory Management Unit for information about the
MMU.
Figure 7-29 is a flowchart of the asynchronous read-modify-write cycle operation. Figure 7-
30 is an example of a functional timing diagram of a TAS instruction specified in terms of
clock periods.
State 0
The processor asserts ECS and OCS in S0 to indicate the beginning of an external
operand cycle. The processor also asserts RMC in S0 to identify a read-modify-write
cycle. The processor places a valid address on A0–A31 and valid function codes on FC0–
FC2. The function codes select the address space for the operation. SIZ0–SIZ1 become
valid in S0 to indicate the operand size. The processor drives R/W high for the read cycle
and sets 4 according to the value of the MMU CI bit in the address translation descriptor
or in the appropriate TTx register.
State 1
One-half clock later in S1, the processor asserts AS, indicating that the address on the
address bus is valid. The processor asserts DS during S1. In addition, the ECS (and OCS,
if asserted) signal is negated during S1.
Bus Operation
7-46 MC68030 USER’S MANUAL MOTOROLA
Figure 7-29. Asynchronous Read-Modify-Write Cycle Flowchart
LOCK BUS
1) ASSERT READ-MODIFY-WRITE
CYCLE (RMC)
ADDRESS DEVICE
1) ASSERT ECS/OCS FOR ONE-HALF CLOCK
2) SET R/W TO READ
3) DRIVE ADDRESS ON A31-A0
4) DRIVE FUNCTION CODE ON FC2- FC0
5) DRIVE SIZE (SIZ1-SIZ0)
6) CACHE INHIBIT OUT (CIOUT) BECOMES VALID
7) ASSERT ADDRESS STROBE (AS)
8) ASSERT DATA STROBE (DS)
9) ASSERT DATA BUFFER ENABLE (DBEN)
ACQUIRE DATA
2) LATCH DATA
3) NEGATE AS AND DS
4) NEGATE DBEN
5) START DATA MODIFICATION
START OUTPUT TRANSFER
1) ASSERT ECS/OCS FOR ONE-HALF CLOCK
2) DRIVE ADDRESS ON A31-A0 (IF DIFFERENT)
3) DRIVE SIZE (SIZ1-SIZ0)
4) SET R/W TO WRITE
5) ASSERT AS
6) ASSERT DBEN
7) PLACE DATA ON D31-D0
8) ASSERT DS
TERMINATE OUTPUT TRANSFER
1) NEGATE AS AND DS
2) REMOVE DATA FROM D31-D0
3) NEGATE DBEN
UNLOCK BUS
1) NEGATE RMC
START NEXT CYCLE
PRESENT DATA
1) DECODE ADDRESS
2) PLACE DATA ON D31-D0
3) ASSERT DATA TRANSFER AND
SIZE ACKNOWLEDGE (DSACKx)
TERMINATE CYCLE
1) REMOVE DATA FROM D31-D0
2) NEGATE DSACKx
ACCEPT DATA
1) DECODE ADDRESS
2) STORE DATA FROM D31-D0
3) ASSERT DSACKx
TERMINATE CYCLE
A
IF CAS2 INSTRUCTION
AND ONLY ONE OPERAND
READ, THEN GO TO A ;
IF OPERANDS DO NOT
MATCH, THEN GO TO
C ; ELSE GO TO
BC
B
1) NEGATE DSACKx
IF CAS2 INSTRUCTION
AND ONLY ONE OPERAND
WRITTEN, THEN GO TO
D ; ELSE GO TO E
E
D
1) SAMPLE CACHE INHIBIT IN
CONTROLLER EXTERNAL DRIVE
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-47
State 2
During state 2 (S2), the processor drives DBEN active to enable external data buffers. The
selected device uses R/W, SIZ0–SIZ1, A0–A1, and DS to place information on the data
bus. Any or all of the bytes (D24–D31, D16–D23, D8–D15, and D0–D7) are selected by
SIZ0–SIZ1 and A0–A1. Concurrently, the selected device may assert the DSACKx
signals.
State 3
As long as at least one of the DSACKx signals is recognized by the end of S2 (meeting
the asynchronous input setup time requirement), data is latched on the next falling edge
of the clock, and the cycle terminates. If DSACKx is not recognized by the start of S3, the
processor inserts wait states instead of proceeding to S4 and S5. To ensure that wait
states are inserted, both DSACK0 and DSACK1 must remain negated throughout the
asynchronous input setup and hold times around the end of S2. If wait states are added,
the processor continues to sample the DSACKx signals on the falling edges of the clock
until one is recognized.
State 4
The processor samples the level of CIIN at the beginning of S4. At the end of S4, the
processor latches the incoming data.
State 5
The processor negates AS, DS, and DBEN during S5. If more than one read cycle is
required to read in the operand(s), S0–S5 are repeated for each read cycle. When
finished reading, the processor holds the address, R/W, and FC0–FC2 valid in
preparation for the write portion of the cycle.
The external device keeps its data and DSACKx signals asserted until it detects the
negation of AS or DS (whichever it detects first). The device must remove the data and
negate DSACKx within approximately one clock period after sensing the negation of AS
or DS. DSACKx signals that remain asserted beyond this limit may be prematurely
detected for the next portion of the operation.
Idle States
The processor does not assert any new control signals during the idle states, but it may
internally begin the modify portion of the cycle at this time. S6-S11 are omitted if no write
cycle is required. If a write cycle is required, the R/W signal remains in the read mode until
S6 to prevent bus conflicts with the preceding read portion of the cycle; the data bus is not
driven until S8.
Bus Operation
7-48 MC68030 USER’S MANUAL MOTOROLA
Figure 7-30. Asynchronous Byte Read-Modify-Write Cycle — 32-Bit Port
(TAS Instruction with CIOUT or CIIN Asserted)
Si
INDIVISIBLE CYCLE NEXT CYCLE
DS
DSACK0
DBEN
D31-D24
DSACK1
D7-D0
D23-D16
OP3
OP3
OP3
OP3
OP3
BERR
HALT
BG
D15-D8
AS
CLK
A31-A2
A1
A0
FC2-FC0
SIZ1
R/W
SIZ0
S0 S2 S4 Si S6 S8 S10 S0
RMC
ECS
CIIN
CIOUT
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-49
State 6
The processor asserts ECS and OCS in S6 to indicate that another external cycle is
beginning. The processor drives R/W low for a write cycle. CIOUT also becomes valid,
indicating the state of the MMU CI bit in the address translation descriptor or in a relevant
TTx register. Depending on the write operation to be performed, the address lines may
change during S6.
State 7
In S7, the processor asserts AS, indicating that the address on the address bus is valid.
The processor also asserts DBEN, which can be used to enable data buffers during S7.
In addition, the ECS (and OCS, if asserted) signal is negated during S7.
State 8
During S8, the processor places the data to be written onto D0–D31.
State 9
The processor asserts DS during S9 indicating that the data is stable on the data bus. As
long as at least one of the DSACKx signals is recognized by the end of S8 (meeting the
asynchronous input setup time requirement), the cycle terminates one clock later. If
DSACKx is not recognized by the start of S9, the processor inserts wait states instead of
proceeding to S10 and S11. To ensure that wait states are inserted, both DSACK0 and
DSACK1 must remain negated throughout the asynchronous input setup and hold times
around the end of S8. If wait states are added, the processor continues to sample
DSACKx signals on the falling edges of the clock until one is recognized.
The selected device uses R/W, DS, SIZ0–SIZ1, and A0–A1 to latch data from the
appropriate section(s) of the data bus (D24–D31, D16–D23, D8–D15, and D0–D7).
SIZ0–SIZ1 and A0–A1 select the data bus sections. If it has not already done so, the
device asserts DSACKx when it has successfully stored the data.
State 10
The processor issues no new control signals during S10.
Bus Operation
7-50 MC68030 USER’S MANUAL MOTOROLA
State 11
The processor negates AS and DS during S11. It holds the address and data valid during
S11 to provide address hold time for memory systems. R/W and FC0–FC2 also remain
valid throughout S11.
If more than one write cycle is required, S6-S11 are repeated for each write cycle.
The external device keeps DSACKx asserted until it detects the negation of AS or DS
(whichever it detects first). The device must remove its data and negate DSACKx within
approximately one clock period after sensing the negation of AS or DS.
7.3.4 Synchronous Read Cycle
A synchronous read cycle is terminated differently from an asynchronous read cycle;
otherwise, the cycles assert and respond to the same signals, in the same sequence.
STERM rather than DSACKx is asserted by the addressed external device to terminate a
synchronous read cycle. Since STERM must meet the synchronous setup and hold times
with respect to all rising edges of the clock while AS is asserted, it does not need to be
synchronized by the processor. Only devices with 32-bit ports may assert STERM. STERM
is also used with the CBREQ and CBACK signals during burst mode operation. It provides
a two-clock (minimum) bus cycle for 32-bit ports and single-clock (minimum) burst accesses,
although wait states can be inserted for these cycles as well. Therefore, a synchronous
cycle terminated with STERM with one wait cycle is a three-clock bus cycle. However, note
that STERM is asserted one-half clock later than DSACKx would be for a similar
asynchronous cycle with zero wait cycles (also three clocks). Thus, if dynamic bus sizing is
not needed, STERM can be used to provide more decision time in an external cache design
than is available with DSACKx for three-clock accesses.
Figure 7-31 is a flowchart of a synchronous long-word read cycle. Byte and word operations
are similar. Figure 7-32 is a functional timing diagram of a synchronous long-word read
cycle.
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-51
State 0
The read cycle starts with S0. The processor drives ECS low, indicating the beginning of
an external cycle. When the cycle is the first cycle of a read operand operation, OCS is
driven low at the same time. During S0, the processor places a valid address on A0–A31
and valid function codes on FC0–FC2. The function codes select the address space for
the cycle. The processor drives R/W high for a read cycle and drives DBEN inactive to
disable the data buffers. SIZ1-SIZ0 become valid, indicating the number of bytes to be
transferred. CIOUT also becomes valid, indicating the state of the MMU CI bit in the
address translation descriptor or in the appropriate TTx register.
State 1
One-half clock later in S1, the processor asserts AS, indicating that the address on the
address bus is valid. The processor also asserts DS during S1. If the burst mode is
enabled for the appropriate on-chip cache and all four long words of the cache entry are
invalid, (i.e., four long words can be read in), CBREQ is asserted. In addition, the ECS
(and OCS, if asserted) signal is negated during S1.
Figure 7-31. Synchronous Long-Word Read Cycle Flowchart —
No Burst Allowed
CONTROLLER
1) ASSERT ECS/OCS FOR ONE-HALF CLOCK
2) DRIVE R/W TO READ
3) DRIVE ADDRESS ON A31–A0
4) DRIVE FUNCTION ON FC2–FC0
5) DRIVE SIZE (SIZ1–SIZ0) (FOUR BYTES)
6) CACHE INHIBIT OUT (CIOUT) BECOMES VALID
7) ASSERT ADDRESS STROBE (AS)
8) ASSERT CACHE BURST REQUEST (CBREQ)
(IF BURST POSSSIBLE)
9) ASSERT DATA STROBE (DS)
10) ASSERT DATA BUFFER ENABLE (DBEN)
1) SAMPLE CACHE INHIBIT IN (CIIN)
AND CACHE BURST ACKNOWLEDGE (CBACK)
2) LATCH DATA
3) NEGATE AS AND DS
4) NEGATE DBEN
PRESENT DATA
1) DECODE ADDRESS
2) PLACE DATA ON D31-D0
3) ASSERT SYNCHRONOUS TERMINATION (STERM)
4) ASSERT CACHE BURST ACKNOWLEDGE (CBACK)
TERMINATE CYCLE
1) REMOVE DATA FROM D31-D0
2) NEGATE STERM
EXTERNAL DEVICE
ADDRESS DEVICE
ACQUIRE DATA
START NEXT CYCLE
Bus Operation
7-52 MC68030 USER’S MANUAL MOTOROLA
State 2
The selected device uses R/W, SIZ0–SIZ1, A0–A1, and CIOUT to place its information on
the data bus. Any or all of the byte sections of the data bus (D24–D31, D16–D23, D8–
D15, and D0–D7) are selected by SIZ0–SIZ1 and A0–A1. During S2, the processor
drives DBEN active to enable external data buffers. In systems that use two-clock
synchronous bus cycles, the timing of DBEN may prevent its use. At the beginning of S2,
the processor samples the level of STERM. If STERM is recognized, the processor
latches the incoming data at the end of S2. If the selected data is not to be cached for the
Figure 7-32. Synchronous Read with CIIN Asserted and CBACK Negated
S0 S2
CLK
A31-A0
D31-D0
ECS
FC2-FC0
SIZ1
SIZ0
R/W
OCS
AS
DS
DSACK1
DSACK0
STERM
CIIN
CIOUT
CBREQ
CBACK
DBEN
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-53
current cycle or if the device cannot supply 32 bits, CIIN must be asserted at the same
time as STERM. In addition, the state of CBACK is latched when STERM is recognized.
Since CIIN, CBACK, and STERM are synchronous signals, they must meet the
synchronous input setup and hold times for all rising edges of the clock while AS is
asserted. If STERM is negated at the beginning of S2, wait states are inserted after S2,
and STERM is sampled on every rising edge thereafter until it is recognized. Once
STERM is recognized, data is latched on the next falling edge of the clock
(corresponding to the beginning of S3).
State 3
The processor negates AS, DS, and DBEN during S3. It holds the address valid during
S3 to simplify memory interfaces. R/W, SIZ0–SIZ1, and FC0–FC2 also remain valid
throughout S3.
The external device must keep its data asserted throughout the synchronous hold time
for data from the beginning of S3. The device must remove its data within one clock
after asserting STERM and negate STERM within two clocks after asserting STERM;
otherwise, the processor may inadvertently use STERM for the next bus cycle.
7.3.5 Synchronous Write Cycle
A synchronous write cycle is terminated differently from an asynchronous write cycle and
the data strobe may not be useful. Otherwise, the cycles assert and respond to the same
signal, in the same sequence. STERM is asserted by the external device to terminate a
synchronous write cycle. The discussion of STERM in the preceding section applies to write
cycles as well as to read cycles.
DS is not asserted for two-clock synchronous write cycles; therefore, the clock (CLK) may
be used as the timing signal for latching the data. In addition, there is no time from the latest
assertion of AS and the required assertion of STERM for any two-clock synchronous bus
cycle. The system must qualify a memory write with the assertion of AS to ensure that the
write is not aborted by internal conditions within the MC68030.
Bus Operation
7-54 MC68030 USER’S MANUAL MOTOROLA
Figure 7-33 is a flowchart of a synchronous write cycle. Figure 7-34 is a functional timing
diagram of this operation with wait states.
State 0
The write cycle starts with S0. The processor drives ECS low, indicating the beginning of
an external cycle. When the cycle is the first cycle of a write operation, OCS is driven low
at the same time. During S0, the processor places a valid address on A0–A31 and valid
function codes on FC0–FC2. The function codes select the address space for the cycle.
The processor drives R/W low for a write cycle. SIZ0–SIZ1 become valid, indicating the
number of bytes to be transferred. CIOUT also becomes valid, indicating the state of the
MMU CI bit in the address translation descriptor or in the appropriate TTx register.
State 1
One-half clock later in S1, the processor asserts AS, indicating that the address on the
address bus is valid. The processor also asserts DBEN during S1, which may be used to
enable the external data buffers. In addition, the ECS (and OCS, if asserted) signal is
negated during S1.
Figure 7-33. Synchronous Write Cycle Flowchart
CONTROLLER
1) ASSERT ECS/OCS FOR ONE-HALF CLOCK
2) DRIVE ADDRESS ON A31–A0
3) DRIVE FUNCTION ON FC2–FC0
4) DRIVE SIZE (SIZ1–SIZ0) (FOUR BYTES)
5) SET R/W TO WRITE
6) CACHE INHIBIT OUT (CIOUT) BECOMES VALID
7) ASSERT ADDRESS STROBE (AS)
8) ASSERT DATA BUFFER ENABLE (DBEN)
ASSERT DATA BUFFER ENABLE (DBEN)
9) DRIVE DATA LINES D31–D0
10) ASSERT DATA STROBE (DS) IF WAIT STATES)
1) NEGATE AS AND DS
2) REMOVE DATA FROM D31-0
3) NEGATE DBEN
1) DECODE ADDRESS
2) STORE DATA ON D31-D0
3) ASSERT SYNCHRONOUS TERMINATION (STERM)
TERMINATE CYCLE
1) NEGATE STERM
EXTERNAL DEVICE
ADDRESS DEVICE
START NEXT CYCLE
TERMINATE OUTPUT TRANSFER
ACCEPT DATA
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-55
State 2
During S2, the processor places the data to be written onto D0–D31. The selected device
uses R/W, CLK, SIZ0–SIZ1, and A0–A1 to latch data from the appropriate section(s) of
the data bus (D24–D31, D16–D23, D8–D15, and D0–D7). SIZ0–SIZ1 and A0–A1 select
the data bus sections. The device asserts STERM when it has successfully stored the
data. If the device does not assert STERM by the rising edge of S2, the processor inserts
wait states until it is recognized. The processor asserts DS at the end of S2 if wait states
are inserted. For zero-wait-state synchronous write cycles, DS is not asserted.
Figure 7-34. Synchronous Write Cycle with Wait States — CIOUT Asserted
CLK
A31-A0
D31-D0
ECS
FC2-FC0
SIZ1
SIZ0
R/W
OCS
AS
DS
DSACK1
DSACK0
STERM
CIIN
CIOUT
CBREQ
CBACK
DBEN
S0 S2 SwS1 Sw S3
Bus Operation
7-56 MC68030 USER’S MANUAL MOTOROLA
State 3
The processor negates AS (and DS, if necessary) during S3. It holds the address and data
valid during S3 to simplify memory interfaces. R/W, SIZ0–SIZ1, FC0–FC2, and DBEN
also remain valid throughout S3.
The addressed device must negate STERM within two clock periods after asserting it, or
the processor may use STERM for the next bus cycle.
7.3.6 Synchronous Read-Modify-Write Cycle
A synchronous read-modify-write operation differs from an asynchronous read-modify-write
operation only in the terminating signal of the read and write cycles and in the use of CLK
instead of DS latching data in the write cycle. Like the asynchronous operation, the
synchronous read-modify-write operation is indivisible. Although the operation is
synchronous, the burst mode is never used during read-modify-write cycles.
Figure 7-35 is a flowchart of the synchronous read-modify-write operation. Timing for the
cycle is shown in Figure 7-36.
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-57
Figure 7-35. Synchronous Read-Modify-Write Cycle Flowchart
1) ASSERT READ-MODIFY-WRITE CYCLE
(RMC)
LOCK BUS
CONTROLLER
START INPUT TRANSFER
1) ASSERT ECS/OCS FOR ONE-HALF CLOCK
2) DRIVE R/W TO READ
3) DRIVE FUNCTION CODE ON FC2–FC0
4) DRIVE ADDRESS ON A31–A0
5) DRIVE SIZE (SIZ1–SIZ0)
6) CACHE INHIBIT OUT (CIOUT) BECOMES
VALID
7) ASSERT ADDRESS STROBE (AS)
8) ASSERT DATA STROBE (DS)
9) ASSERT DATA BUFFER ENABLE (DBEN)
TERMINATE INPUT TRANSFER
1) SAMPLE CACHE INHIBIT IN (CIIN)
2) LATCH DATA
3) NEGATE AS AND DS
4) NEGATE DBEN
5) START DATA MODICIATION
START OUTPUT TRANSFER
1) ASSERT ECS/OCS FOR ONE-HALF CLOCK
2) SET R/W TO WRITE
3) DRIVE ADDRESS ON A31–A0 (IF DIFFERENT)
4) DRIVE SIZE (SIZ1–SIZ0)
5) CIOUT BECOMES VALID
6) ASSERT AS
7) ASSERT DBEN
8) PLACE DATA ON D31–D0
9) ASSERT DS (IF WAIT STATES)
TERMINATE OUTPUT TRANSFER
1) NEGATE AS (AND DS)
2) REMOVE DATA FROM D31–D0
3) NEGATE DBEN
UNLOCK BUS
1) NEGATE RMC
START NEXT CYCLE
PRESENT DATA
1) DECODE ADDRESS
2) PLACE DATA ON D31-D0
3) ASSERT SYNCHRONOUS
TERMINATION (STERM)
TERMINATE CYCLE
1) REMOVE DATA FROM D31–D0
2) NEGATE STERM
ACCEPT DATA
TERMINATE CYCLE
1) DECODE ADDRESS
2) STORE DATA FROM D31-D0
3) ASSERT STERM
1) NEGATE STERM
IF CAS2 INSTRUCTION
AND ONLY ONE
OPERAND
WRITTEN, THEN GO TO
D : ELSE GO TO E
E
D
IF CAS2 INSTRUCTION
AND ONLY ONE OPERAND
READ, THEN GO TO A :
IF OPERANDS DO NOT
MATCH, THEN GO TO C :
ELSE GO TO B
A
C
B
EXTERNAL DEVICE
Bus Operation
7-58 MC68030 USER’S MANUAL MOTOROLA
State 0
The processor asserts ECS and OCS in S0 to indicate the beginning of an external
operand cycle. The processor also asserts RMC in S0 to identify a read-modify-write
cycle. The processor places a valid address on A0–A31 and valid function codes on FC0–
FC2. The function codes select the address space for the operation. SIZ0–SIZ1 become
valid in S0 to indicate the operand size. The processor drives R/W high for a read cycle
Figure 7-36. Synchronous Read-Modify-Write Cycle Timing — CIIN Asserted
S0 S2 SiS1 S3 Si S4 S5 S6 S7
CLK
A31-A0
D31-D0
ECS
FC2-FC0
SIZ1
SIZ0
R/W
OCS
AS
DS
DSACK1
DSACK0
STERM
CIIN
CIOUT
CBREQ
CBACK
DBEN
RMC
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-59
and sets CIOUT to the value of the MMU CI bit in the address translation descriptor or in
the appropriate TTx register. The processor drives DBEN inactive to disable the data
buffers.
State 1
One-half clock later in S1, the processor asserts AS, indicating that the address on the
address bus is valid. The processor also asserts DS during S1. In addition, the ECS (and
OCS, if asserted) signal is negated during S1.
State 2
The selected device uses R/W, SIZ0–SIZ1, A0–A1, and CIOUT to place its information on
the data bus. Any or all of the byte sections (D24–D31, D16–D23, D8–D15, and D0–D7)
are selected by SIZ0–SIZ1 and A0–A1. During S2, the processor drives DBEN active to
enable external data buffers. In systems that use two-clock synchronous bus cycles, the
timing of DBEN may prevent its use. At the beginning of S2, the processor samples the
level of STERM. If STERM is recognized, the processor latches the incoming data. If the
selected data is not to be cached for the current cycle or if the device cannot supply 32
bits, CIIN must be asserted at the same time as STERM.
Since CIIN and STERM are synchronous signals, they must meet the synchronous nput
setup and hold times for all rising edges of the clock while AS is asserted. If STERM is
negated at the beginning of S2, wait states are inserted after S2, and STERM is sampled
on every rising edge thereafter until it is recognized. Once STERM is recognized, data is
latched on the next falling edge of the clock (corresponding to the beginning of S3).
Bus Operation
7-60 MC68030 USER’S MANUAL MOTOROLA
State 3
The processor negates AS, DS, and DBEN during S3. If more than one read cycle is
required to read in the operand(s), S0–S3 are repeated accordingly. When finished with
the read cycle, the processor holds the address, R/W, and FC0–FC2 valid in preparation
for the write portion of the cycle.
The external device must keep its data asserted throughout the synchronous hold time for
data from the beginning of S3. The device must remove the data within one-clock cycle
after asserting STERM to avoid bus contention. It must also negate STERM within two
clocks after asserting STERM; otherwise, the processor may inadvertently use STERM
for the next bus cycle.
Idle States
The processor does not assert any new control signals during the idle states, but it may
begin the modify portion of the cycle at this time. The R/W signal remains in the read mode
until S4 to prevent bus conflicts with the preceding read portion of the cycle; the data bus
is not driven until S6.
State 4
The processor asserts ECS and OCS in S4 to indicate that an external cycle is beginning.
The processor drives R/W low for a write cycle. CIOUT also becomes valid, indicating the
state of the MMU CI bit in the address translation descriptor or in the appropriate TTx
register. Depending on the write operation to be performed, the address lines may change
during S4.
State 5
In state 5 (S5), the processor asserts AS to indicate that the address on the address bus
is valid. The processor also asserts DBEN during S5, which can be used to enable
external data buffers.
State 6
During S6, the processor places the data to be written onto the D0–D31.
The selected device uses R/W, CLK, SIZ0–SIZ1, and A0–A1 to latch data from the
appropriate byte(s) of the data bus (D24–D31, D16–D23, D8–D15, and D0–D7). SIZ0–
SIZ1 and A0–A1 select the data bus sections. The device asserts STERM when it has
successfully stored the data. If the device does not assert STERM by the rising edge of
S6, the processor inserts wait states until it is recognized. The processor asserts DS at
the end of S6 if wait states are inserted. Note that for zero-wait-state synchronous write
cycles, DS is not asserted.
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-61
State 7
The processor negates AS (and DS, if necessary) during S7. It holds the address and
data valid during S7 to simplify memory interfaces. R/W and FC0–FC2 also remain valid
throughout S7.
If more than one write cycle is required, S8-S11 are repeated for each write cycle.
The external device must negate STERM within two clock periods after asserting it, or the
processor may inadvertently use STERM for the next bus cycle.
7.3.7 Burst Operation Cycles
The MC68030 supports a burst mode for filling the on-chip instruction and data caches.
The MC68030 provides a set of handshake control signals for the burst mode. When a miss
occurs in one of the caches, the MC68030 initiates a bus cycle to obtain the required data
or instruction stream fetch. If the data or instruction can be cached, the MC68030 attempts
to fill a cache entry. Depending on the alignment for a data access, the MC68030 may
attempt to fill two cache entries. The processor may also assert CBREQ to request a burst
fill operation. That is, the processor can fill additional entries in the line. The MC68030 allows
a burst of as many as four long words.
The mechanism that asserts the CBREQ signal for burstable cache entries is enabled by
the data burst enable (DBE) and instruction burst enable (IBE) bits of the cache control
register (CACR) for the data and instruction caches, respectively. Either of the following
conditions cause the MC68030 to initiate a cache burst request (and assert CBREQ) for a
cachable read cycle:
• The logical address and function code signals of the current instruction or data fetch do
not match the indexed tag field in the respective instruction or data cache.
• All four long words corresponding to the indexed tag in the appropriate cache are
marked invalid.
However, the MC68030 does not assert CBREQ during the first portion of a misaligned
access if the remainder of the access does not correspond to the same cache line. Refer to
6.1.3.1 Single Entry Mode for details.
Bus Operation
7-62 MC68030 USER’S MANUAL MOTOROLA
If the appropriate cache is not enabled or if the cache freeze bit for the cache is set, the
processor does not assert CBREQ. CBREQ is not asserted during the read or write cycles
of any read-modify-write operation.
The MC68030 allows burst filling only from 32-bit ports that terminate bus cycles with
STERM and respond to CBREQ by asserting CBACK. When the MC68030 recognizes
STERM and CBACK and it has asserted CBREQ, it maintains AS, DS, R/W, A0–A31, FC0–
FC2, SIZ0–SIZ1 in their current state throughout the burst operation. The processor
continues to accept data on every clock during which STERM is asserted until the burst is
complete or an abnormal termination occurs.
CBACK indicates that the addressed device can respond to a cache burst request by
supplying one more long word of data in the burst mode. It can be asserted independently
of the CBREQ signal, and burst mode is only initiated if both of these signals are asserted
for a synchronous cycle. If the MC68030 executes a full burst operation and fetches four
long words, CBREQ is negated after STERM is asserted for the third cycle, indicating that
the MC68030 only requests one more long word (the fourth cycle). CBACK can then be
negated, and the MC68030 latches the data for the fourth cycle and completes the cache
line fill.
The following conditions can abort a burst fill:
• CIIN asserted,
• BERR asserted, or
• CBACK negated prematurely.
The processing of a bus error during a burst fill operation is described in 7.5.1 Bus Errors.
For the purposes of halting the processor or arbitrating the bus away from the processor with
BR, a burst operation is a single cycle since AS remains asserted during the entire
operation. If the HALT signal is asserted during a burst operation, the processor halts at the
end of the operation. Refer to 7.5.3 Halt Operation for more information about the halt
operation. An alternate bus master requesting the bus with BR may become bus master at
the end of the operation provided BR is asserted early enough to be internally synchronized
before another processor cycle begins. Refer to 7.7 Bus Arbitration for more information
about bus arbitration.
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-63
The simultaneous assertion of BERR and HALT during a bus cycle normally indicates that
the cycle should be retried. However, during the second, third, or fourth cycle of a burst
operation, this signal combination indicates a bus error condition, which aborts the burst
operation. In addition, the processor remains in the halted state until HALT is negated. For
information about bus error processing, refer to 7.5.1 Bus Errors.
Figure 7-37 is a flowchart of the burst operation. The following timing diagrams show various
burst operations. Figure 7-38 shows burst operations for long-word requests with two wait
states inserted in the first access and one wait cycle inserted in the subsequent accesses.
Figure 7-39 shows a burst operation that fails to complete normally due to CBACK negating
prematurely. Figure 7-40 shows a burst operation that is deferred because the entire
operand does not correspond to the same cache line. Figure 7-41 shows a burst operation
aborted by CIIN. Because CBACK corresponds to the next cycle, three long words are
transferred even though CBACK is only asserted for two clock periods.
The burst operation sequence begins with states S0–S3, which are very similar to those
states for a synchronous read cycle except that CBREQ is asserted. S4-S9 perform the final
three reads for a complete burst operation.
State 0
The burst operation starts with S0. The processor drives ECS low, indicating the
beginning of an external cycle. When the cycle is the first cycle of a read operation, OCS
is driven low at the same time. During S0, the processor places a valid address on A0–
A31 and valid function codes on FC0–FC2. The function codes select the address space
for the cycle. The processor drives R/W high, indicating a read cycle, and drives DBEN
inactive to disable the data buffers. SIZ0–SIZ1 become valid, indicating the number of
operand bytes to be transferred. CIOUT also becomes valid, indicating the state of the
MMU CI bit in the address translation descriptor or in the appropriate TTx register.
State 1
One-half clock later in S1, the processor asserts AS to indicate that the address on the
address bus is valid. The processor also asserts DS during S1. CBREQ is also asserted,
indicating that the MC68030 can perform a burst operation into one of its caches and can
read in four long words. In addition, ECS (and OCS, if asserted) is negated during S1.
State 2
The selected device uses R/W, SIZ0–SIZ1, A0–A1, and CIOUT to place the data on the
data bus. (The first cycle must supply the long word at the corresponding long-word
boundary.) All of the byte sections (D24–D31, D16–D23, D8–D15, and D0–D7) of the data
bus must be driven since the burst operation latches 32 bits on every cycle. During S2,
the processor drives DBEN active to enable external data buffers. In systems that use
two-clock synchronous bus cycles, the timing of DBEN may prevent its use. At the
beginning of S2, the processor tests the level of STERM. If STERM is recognized, the
processor latches the incoming data at the end of S2. For the burst operation to proceed,
CBACK must be asserted when STERM is recognized. If the data for the current cycle is
Bus Operation
7-64 MC68030 USER’S MANUAL MOTOROLA
not to be cached, CIIN must be asserted at the same time as STERM. The assertion of
CIIN also has the effect of aborting the burst operation.
Figure 7-37. Burst Operation Flowchart — Four Long Words Transferred
END OF BURST
1) NEGATE AS AND DS
2) NEGATE DBEN
CONTROLLER
1) ASSERT ECS/OCS FOR ONE-HALF CLOCK
2) DRIVE R/W TO READ
3) DRIVE ADDRESS ON A31–A0
4) DRIVE FUNCTION ON FC2–FC0
5) DRIVE SIZE (SIZ1–SIZ0) (FOUR BYTES)
6) CACHE INHIBIT OUT (CIOUT) BECOMES
VALID
7) ASSERT ADDRESS STROBE (AS)
8) ASSERT CACHE BURST REQUEST (CBREQ)
9) ASSERT DATA STROBE (DS)
10) ASSERT DATA BUFFER ENABLE (DBEN)
1) SAMPLE CACHE INHIBIT IN (CIIN)
AND CACHE BURST ACKNOWLEDGE
(CBACK)
2) LATCH DATA
PRESENT DATA
1) DECODE ADDRESS
2) PLACE DATA ON D31-D0
3) ASSERT SYNCHRONOUS TERMINATION (STERM)
4) ASSERT CACHE BURST ACKNOWLEDGE (CBACK)
TERMINATE CYCLE
1) REMOVE DATA FROM D31-D0
2) NEGATE STERM (IF NECESSARY)
3) NEGATE CBACK (IF NECESSARY)
EXTERNAL DEVICE
ADDRESS DEVICE
ACQUIRE DATA
WHEN 4 LONG WORDS TRANSFERRED UNTIL 4 LONG WORDS TRANSFERRED
START NEXT CYCLE
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-65
Figure 7-38. Long-Word Operand Request from $07 with
Burst Request and Wait Cycle
S0 S2 SwS1 Sw Sw Sw SwS4 S5 Sw SwS6 S9S8SwS7
b4–b7 bC–bFbC–bFb8–bB
SwSw SwSw S3
A31-A4
A3
A2–A0
FC2-FC0
R/W
ECS
OCS
CLK
AS
DS
STERM
CBREQ
CBACK
D31–D0
DBEN
SIZ1–SIZ0
CIIN
CIOUT
01 10 11 00
VALUE OF A3:A2 INCREMENTED BY THE SYSTEM HARDWARE
Bus Operation
7-66 MC68030 USER’S MANUAL MOTOROLA
Figure 7-39. Long-Word Operand Request from $07 with
Burst Request — CBACK Negated Early
CLK
A31–A4
A3
A2–A0
FC2–FC0
SIZ1–SIZ0
R/W
S0 S2 S4 S6
ECS
OCS
AS
DS
b4–b7 b8–bB bC–bF
01 10 11
12
VALUE OF CBACK
CONTROL NEXT CYCLE
3
STERM
CIIN
CIOUT
CBREQ
CBACK
D31–D0
DBEN
VALUE OF A3:A2 INCREMENTED BY THE SYSTEM HARDWARE
NOTES:
1. Assertion of CBACK causes data to be placed on D31–D0.
2. Continued assertion of CBACK causes data to be placed on D31–D0.
3. Negation of CBACK causes AS to be negated.
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-67
Figure 7-40. Long-Word Operand Request from $0E — Burst Fill Deferred
A31-A5
A4
A3–A1
FC2-FC0
SIZ1
R/W
ECS
OCS
CLK
S0 S2 Sw S0S1 Sw S3 S1 S2 Sw Sw S3 Sw Sw S4 S5 Sw Sw S6 S9S8SwSwS7
A0
SIZ0
AS
DS
STERM
CBREQ
CBACK
D31–D0
DBEN
b4–b7 bC–bF
bC–bF b0–b3 b8–bB
PREVIOUS CACHE BLOCK NEXT CACHE BLOCK - START BURST CYCLE
Bus Operation
7-68 MC68030 USER’S MANUAL MOTOROLA
Figure 7-41. Long-Word Operand Request from $07 with
Burst Request — CBACK and CIIN Asserted
A31–A0
FC2–FC0
R/W
ECS
OCS
CLK
S0 S2
AS
DS
STERM
CBREQ
CBACK
D31–D0
DBEN
CIIN
CIOUT
S4
SIZ1
SIZ0
DSACK1
DSACK0
b4-b7
BURST MODE ENDS,
DATA NOT CACHED
01 10 11
VALUE OF A3:A2 INCREMENTED BY THE SYSTEM HARDWARE
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-69
Since CIIN, CBACK, and STERM are synchronous signals, they must meet the
synchronous input setup and hold times for all rising edges of the clock while AS is
asserted. If STERM is negated at the beginning of S2, wait states are inserted after S2,
and STERM is sampled on every rising edge of the clock thereafter until it is recognized.
Once STERM is recognized, data is latched on the next falling edge of the clock
(corresponding to the beginning of S3).
State 3
The processor maintains AS, DS, and DBEN asserted during S3. It also holds the address
valid during S3 for continuation of the burst. R/W, SIZ0–SIZ1, and FC0–FC2 also remain
valid throughout S3.
The external device must keep the data driven throughout the synchronous hold time for
data from the beginning of S3. The device must negate STERM within one clock after
asserting STERM; otherwise, the processor may inadvertently use STERM prematurely
for the next burst access. STERM need not be negated if subsequent accesses do not
require wait cycles.
State 4
At the beginning of S4, the processor tests the level of STERM. This state signifies the
beginning of burst mode, and the remaining states correspond to burst fill cycles. If
STERM is recognized, the processor latches the incoming data at the end of S4. This data
corresponds to the second long word of the burst. If STERM is negated at the beginning
of S4, wait states are inserted instead of S4 and S5, and STERM is sampled on every
rising edge of the clock thereafter until it is recognized. As for synchronous cycles, the
states of CBACK and CIIN are latched at the time STERM is recognized. The assertion
of CBACK at this time indicates that the burst operation should continue, and the assertion
of CIIN indicates that the data latched at the end of S4 should not be cached and that the
burst should abort.
State 5
The processor maintains all the signals on the bus driven throughout S5 for continuation
of the burst. The same hold times for STERM and data described for S3 apply here.
State 6
This state is identical to S4 except that once STERM is recognized, the third long word of
data for the burst is latched at the end of S6.
Bus Operation
7-70 MC68030 USER’S MANUAL MOTOROLA
State 7
During this state, the processor negates CBREQ, and the memory device may negate
CBACK. Aside from this, all other bus signals driven by the processor remain driven.
The same hold times for STERM and data described for S3 apply here.
State 8
This state is identical to S4 except that CBREQ is negated, indicating that the processor
cannot continue to accept more data after this. The data latched at the end of S8
corresponds to the fourth long word of the burst.
State 9
The processor negates AS, DS, and DBEN during S9. It holds the address, R/W, SIZ0–
SIZ1, and FC0–FC2 valid throughout S9. The same hold times for data described for S3
apply here.
Note that the address bus of the MC68030 remains driven to a constant value for the
duration of a burst transfer operation (including the first transfer before burst mode is
entered). If an external memory system requires incrementing of the long-word base
address to supply successive long words of information, this function must be performed by
external hardware. Additionally, in the case of burst transfers that cross a 16-byte boundary
(i.e., the first long word transferred is not located at A3/A2=00), the external hardware must
correctly control the continuation or termination of the burst transfer as desired. The burst
may be terminated by negating CBACK during the transfer of the most significant long word
of the 16-byte image (A3/A2=11) or may be continued (with CBACK asserted) by providing
the long word located at A3/A2=00 (i.e., the count sequence wraps back to zero and
continues as necessary). The MC68030 caches assume the higher order address lines (A4-
A31) remain unchanged as the long-word accesses wrap back around to A3/A2=00.
7.4 CPU SPACE CYCLES
FC0–FC2 select user and supervisor program and data areas as listed in Table 4-1. The
area selected by FC0–FC2=$7 is classified as the CPU space. The interrupt acknowledge,
breakpoint acknowledge, and coprocessor communication cycles described in the following
sections utilize CPU space.
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-71
The CPU space type is encoded on A16-A19 during a CPU space operation and indicates
the function that the processor is performing. On the MC68030, three of the encodings are
implemented as shown in Figure 7-42. All unused values are reserved by Motorola for future
additional CPU space types.
7.4.1 Interrupt Acknowledge Bus Cycles
When a peripheral device signals the processor (with the IPL0–IPL2 signals) that the device
requires service, and the internally synchronized value on these signals indicates a higher
priority than the interrupt mask in the status register (or that a transition has occurred in the
case of a level 7 interrupt), the processor makes the interrupt a pending interrupt. Refer to
8.1.9 Interrupt Exceptions for details on the recognition of interrupts.
The MC68030 takes an interrupt exception for a pending interrupt within one instruction
boundary (after processing any other pending exception with a higher priority). The following
paragraphs describe the various kinds of interrupt acknowledge bus cycles that can be
executed as part of interrupt exception processing.
Figure 7-42. MC68030 CPU Space Address Encoding
1 1 1
1 1 1
1 1 1
BREAKPOINT
ACKNOWLEDGE
COPROCESSOR
COMM.
INTERRUPT
ACKNOWLEDGE 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 LEVEL 1
0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 CPID 0 0 0 0 0 0 0 0 CP REG
15 13 4 0
31031
31
BKPT # 0 0
31 420
0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
19 162320
FUNCTION
CODE ADDRESS BUS
CPU SPACE
TYPE FIELD
Bus Operation
7-72 MC68030 USER’S MANUAL MOTOROLA
7.4.1.1 INTERRUPT ACKNOWLEDGE CYCLE — TERMINATED NORMALLY. When
the MC68030 processes an interrupt exception, it performs an interrupt acknowledge cycle
to obtain the number of the vector that contains the starting location of the interrupt service
routine.
Some interrupting devices have programmable vector registers that contain the interrupt
vectors for the routines they use. The following paragraphs describe the interrupt
acknowledge cycle for these devices. Other interrupting conditions or devices cannot supply
a vector number and use the autovector cycle described in 7.4.1.2 Autovector Interrupt
Acknowledge Cycle.
The interrupt acknowledge cycle is a read cycle. It differs from the asynchronous read cycle
described in 7.3.1 Asynchronous Read Cycle or the synchronous read cycle described in
7.3.4 Synchronous Read Cycle in that it accesses the CPU address space. Specifically,
the differences are:
1. FC0–FC2 are set to seven (FC0/FC1/FC2=111) for CPU address space.
2. A1, A2, and A3 are set to the interrupt request level (the inverted values of IPL0, iPL1,
and IPL2, respectively).
3. The CPU space type field (A16-A19) is set to $F, the interrupt acknowledge code.
4. A20–A31, A4–A15, and A0 are set to one.
The responding device places the vector number on the data bus during the interrupt
acknowledge cycle. Beyond this, the cycle is terminated normally with either STERM or
DSACKx. Figure 7-43 is the flowchart of the interrupt acknowledge cycle.
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-73
Figure 7-44 shows the timing for an interrupt acknowledge cycle terminated with DSACKx.
7.4.1.2 AUTOVECTOR INTERRUPT ACKNOWLEDGE CYCLE. When the interrupting
device cannot supply a vector number, it requests an automatically generated vector or
autovector. Instead of placing a vector number on the data bus and asserting DSACKx or
STERM, the device asserts the autovector signal (AVEC) to terminate the cycle. Neither
STERM nor DSACKx may be asserted during an interrupt acknowledge cycle terminated by
AVEC.
The vector number supplied in an autovector operation is derived from the interrupt level of
the current interrupt. When AVEC is asserted instead of DSACK or STERM during an
interrupt acknowledge cycle, the MC68030 ignores the state of the data bus and internally
generates the vector number, the sum of the interrupt level plus 24 ($18). There are seven
distinct autovectors that can be used, corresponding to the seven levels of interrupt
available with signals IPL0–IPL2. Figure 7-45 shows the timing for an autovector operation.
Figure 7-43. Interrupt Acknowledge Cycle Flowchart
REQUEST INTERRUPT
INTERRUPTING DEVICECONTROLLER
1) PLACE VECTOR NUMBER ON LEAST
SIGNIFICANT BYTE OF DATA PORT
(DEPENDS ON PORT SIZE)
2) ASSERT DATA AND SIZE ACKNOWLEDGE
(DSACKx)
OR
ASSERT SYNCHRONOUS TERMINATION
(STERM)
PROVIDE VECTOR INFORMATION
ACKNOWLEDGE INTERRUPT
1) INTERRUPT PENDING (IPEND) RECOGNIZED BY
CURRENT INSTRUCTION – WAIT FOR
INSTRUCTION BOUNDARY
2) SET R/W TO READ
3) SET FUNCTION CODE TO CPU SPACE
4) PLACE INTERRUPT LEVEL ON A1,A2, AND A3.
TYPE FIELD = INTERRUPT ACKNOWLEDGE (IACK)
5) SET SIZE TO BYTE
6) NEGATE IPEND
7) ASSERT ADDRESS STROBE (AS) AND DATA
STROBE (DS)
ACQUIRE VECTOR NUMBER
1) LATCH VECTOR NUMBER
2) NEGATE AS AND DS
CONTINUE INTERRUPT EXCEPTION PROCESSING
RELEASE
1) REMOVE VECTOR NUMBER FROM DATA BUS
2) NEGATE DSACKx
Bus Operation
7-74 MC68030 USER’S MANUAL MOTOROLA
Figure 7-44. Interrupt Acknowledge Cycle Timing
READ CYCLE INTERRUPT
ACKNOWLEDGE WRITE STACK
CLK
A31-A4
A3-A1
A0
FC2-FC0
SIZ1
R/W
ECS
OCS
AS
DS
DSACK0
DBEN
D31-D24
IPL2-IPL0
SIZ0
DSACK1
S0 S2 S4 S0 S2 S4 S0 S2
INTERRUPT LEVEL
IPEND
D7-D0
D23-D16
VECTOR # FROM 8-BIT PORT
VECTOR # FROM 16-BIT PORT
VECTOR # FROM 32-BIT PORT
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-75
Figure 7-45. Autovector Operation Timing
READ CYCLE INTERRUPT
ACKNOWLEDGE
AUTOVECTORED WRITE STACK
CLK
A31-A4
A3-A1
A0
FC2-FC0
SIZ1
R/W
ECS
OCS
AS
DS
DSACK0
DBEN
D31-D0
IPL2-IPL0
AVEC
SIZ0
DSACK1
S0 S2 S4 S0 S2 S4 S0 S2
INTERRUPT LEVEL
Bus Operation
7-76 MC68030 USER’S MANUAL MOTOROLA
7.4.1.3 SPURIOUS INTERRUPT CYCLE. When a device does not respond to an interrupt
acknowledge cycle with AVEC, STERM, or DSACKx, the external logic typically returns
BERR. The MC68030 automatically generates the spurious interrupt vector number, 24,
instead of the interrupt vector number in this case. If HALT is also asserted, the processor
retries the cycle.
7.4.2 Breakpoint Acknowledge Cycle
The breakpoint acknowledge cycle is generated by the execution of a breakpoint instruction
(BKPT). The breakpoint acknowledge cycle allows the external hardware to provide an
instruction word directly into the instruction pipeline as the program executes. This cycle
accesses the CPU space with a type field of zero and provides the breakpoint number
specified by the instruction on address lines A2–A4. If the external hardware terminates the
cycle with DSACKx or STERM, the data on the bus (an instruction word) is inserted into the
instruction pipe, replacing the breakpoint opcode, and is executed after the breakpoint
acknowledge cycle completes. The breakpoint instruction requires a word to be transferred
so that if the first bus cycle accesses an 8-bit port, a second cycle is required. If the external
logic terminates the breakpoint acknowledge cycle with BERR (i.e., no instruction word
available), the processor takes an illegal instruction exception. Figure 7-46 is a flowchart of
the breakpoint acknowledge cycle. Figure 7-47 shows the timing for a breakpoint
acknowledge cycle that returns an instruction word. Figure 7-48 shows the timing for a
breakpoint acknowledge cycle that signals an exception.
7.4.3 Coprocessor Communication Cycles
The MC68030 coprocessor interface provides instruction-oriented communication between
the processor and as many as seven coprocessors. The bus communication required to
support coprocessor operations uses the MC68030 CPU space with a type field of $2.
Coprocessor accesses use the MC68030 bus protocol except that the address bus supplies
access information rather than a 32-bit address. The CPU space type field (A16-A19) for a
coprocessor operation is $2. A13-A15 contain the coprocessor identification number (CpID),
and A0–A4 specify the coprocessor interface register to be accessed. Coprocessor
accesses to a CpID of zero correspond to MMU instructions and are not generated by the
MC68030 as a result of the coprocessor interface. These cycles can only be generated by
the MOVES instruction. Refer to Section 10 Coprocessor Interface Description for
further information.
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-77
7.5 BUS EXCEPTION CONTROL CYCLES
The MC68030 bus architecture requires assertion of either DSACKx or STERM from an
external device to signal that a bus cycle is complete. DSACKx, STERM, or AVEC is not
asserted if:
• The external device does not respond.
• No interrupt vector is provided.
• Various other application-dependent errors occur.
External circuitry can provide BERR when no device responds by asserting DSACKx,
STERM, or AVEC within an appropriate period of time after the processor asserts AS. This
allows the cycle to terminate and the processor to enter exception processing for the error
condition.
The MMU can also detect an internal bus error. This occurs when the processor attempts to
access an address in a protected area of memory (a user program attempts to access
supervisor data, for example) or after the MMU receives a bus error while searching the
address table for an address translation description.
Figure 7-46. Breakpoint Operation Flow
1) PLACE REPLACEMENT OPCODE ON DATA
BUS
2) ASSERT DATA TRANSFER AND SIZE
ACKNOWLEDGE (DSACKx) SYNCHRONOUS
TERMINATION (STERM)
OR
1) ASSERT BUS ERRROR (BERR) TO INITIATE
EXCEPTION PROCESSING
CONTROLLER
1) SET R/W TO READ
2) SET FUNCTION CODE TO CPU SPACE
3) PLACE CPU SPACE TYPE 0 ON A19-A16
4) PLACE BREAKPOINT NUMBER ON A4-A2
5) SET SIZE TO WORD
6) ASSERT ADDRESS STROBE (AS) AND DATA
STROBE (DS)
BREAKPOINT ACKNOWLEDGE
1) PLACE LATCHED DATA IN INSTRUCTION
PIPELINE
2) CONTINUE PROCESSING
1) INITIATE ILLEGAL INSTRUCTION PROCESSING
SLAVE NEGATES DSACKx, STERM OR BERR
EXTERNAL DEVICE
IF DSACKx OR STERM
1) LATCH DATA
2) NEGATE AS AND DS
3) GO TO A
IF BERR ASSERTED:
1) NEGATE AS AND DS
2) GO TO B A B
Bus Operation
7-78 MC68030 USER’S MANUAL MOTOROLA
Figure 7-47. Breakpoint Acknowledge Cycle Timing
BREAKPOINT
ACKNOWLEDGE
INSTRUCTION WORD
FETCH
READ CYCLE
CLK
A31-A20
A19-A16
A15-A2
FC2-FC0
SIZ1
R/W
ECS
OCS
AS
DSACK0
D31-D24
D23-D16
SIZ0
DSACK1
S0 S2 S4 S0 S2 S4 S0 S2
D7-D0
D15-D8
BREAKPOINT NUMBER
WORD
FETCHED
INSTRUCTION
EXECUTION
(0000)
BREAKPOINT ENCODING
A1-A0
HALT
BERR
CPU SPACE
DS
DBEN
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-79
Another signal that is used for bus exception control is HALT. This signal can be asserted
by an external device for debugging purposes to cause single bus cycle operation or (in
combination with BERR) a retry of a bus cycle in error.
Figure 7-48. Breakpoint Acknowledge Cycle Timing (Exception Signaled)
CLK
A31-A0
FC2-FC0
R/W
ECS
OCS
AS
DS
DSACK0
DBEN
SIZ1-SIZ0
DSACK1
S0 S2 S4 S0 S2
HALT
SwSw Sw S4
D31-D0
BERR
READ WITH BUS ERROR ASSERTED INTERNAL
PROCESSING STACK WRITE
Bus Operation
7-80 MC68030 USER’S MANUAL MOTOROLA
To properly control termination of a bus cycle for a retry or a bus error condition, DSACKx,
BERR, and HALT can be asserted and negated with the rising edge of the MC68030 clock.
This assures that when two signals are asserted simultaneously, the required setup time
(#47A) and hold time (#47B) for both of them is met for the same falling edge of the
processor clock. (Refer to MC68030EC/D, MC68030 Electrical Specifications for timing
requirements.) This or some equivalent precaution should be designed into the external
circuitry that provides these signals.
The acceptable bus cycle terminations for asynchronous cycles are summarized in relation
to DSACKx assertion as follows (case numbers refer to Table 7-8):
Normal Termination:
DSACKx is asserted; BERR and HALT remain negated (case 1).
Halt Termination:
HALT is asserted at same time or before DSACKx, and BERR remains negated (case
2).
Bus Error Termination:
BERR is asserted in lieu of, at the same time, or before DSACKx (case 3) or after
DSACKx (case 4), and HALT remains negated; BERR is negated at the same time or
after DSACKx.
Retry Termination:
HALT and BERR are asserted in lieu of, at the same time, or before DSACKx (case 5)
or after DSACKx (case 6); BERR is negated at the same time or after DSACKx; HALT
may be negated at the same time or after BERR.
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-81
LEGEND:
N — The number of current even bus state (e.g., S2, S4, etc.)
A — Signal is asserted in this bus state
NA — Signal is not asserted in this state
X — Don't care
S — Signal was asserted in previous state and remains asserted in this state
Table 7-8 shows various combinations of control signal sequences and the resulting bus
cycle terminations. To ensure predictable operation, BERR and HALT should be negated
according to the specifications in MC68030EC/D,
MC68030 Electrical Specifications
.
DSACKx, BERR, and HALT may be negated after AS. If DSACKx or BERR remain asserted
into S2 of the next bus cycle, that cycle may be terminated prematurely.
The termination signal for a synchronous cycle is STERM. An analogous set of bus cycle
termination cases exists in relationship to STERM assertion. Note that STERM and
DSACKx must never both be asserted in the same cycle. STERM has setup time (#60) and
hold time (#61) requirements relative to each rising edge of the processor clock while AS is
asserted. Bus error and retry terminations during burst cycles operate as described in
6.1.3.2 Burst Mode Filling, 7.5.1 Bus Errors, and 7.5.2 Retry Operation.
Table 7-8. DSACK, BERR, and HALT Assertion Results
Case
No. Control
Signal Asserted on Rising
Edge of State Result
N N+2
1 DSACKx
BERR
HALT
A
NA
NA
S
NA
X
Normal cycle terminate and continue.
2 DSACKx
BERR
HALT
A
NA
A/S
S
NA
S
Normal cycle terminate and halt. Continue when HALT
negated.
3 DSACKx
BERR
HALT
NA/A
A
NA
X
S
NA
Terminate and take bus error exception, possibly
deferred.
4 DSACKx
BERR
HALT
A
NA
NA
X
A
NA
Terminate and take bus error exception, possibly
deferred.
5 DSACKx
BERR
HALT
NA/A
A
A/S
X
S
S
Terminate and retry when HALT negated.
6 DSACKx
BERR
HALT
A
NA
NA
X
A
A
Terminate and retry when HALT negated.
Bus Operation
7-82 MC68030 USER’S MANUAL MOTOROLA
For STERM, the bus cycle terminations are summarized as follows (case numbers refer to
Table 7-9):
Normal Termination:
STERM is asserted; BERR and HALT remain negated (case 1).
Halt Termination:
HALT is asserted before STERM, and BERR remains negated (case 2).
Bus Error Termination:
BERR is asserted in lieu of, at the same time, or before STERM (case 3) or after
STERM (case 4), and HALT remains negated; BERR is negated at the same time or
after STERM.
Retry Termination:
HALT and BERR are asserted in lieu of, at the same time, or before STERM (case 5)
or after STERM (case 6); BERR is negated at the same time or after STERM; HALT
may be negated at the same time or after BERR.
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-83
LEGEND:
N —The number of current even bus state (e.g., S2, S4, etc.)
A —Signal is asserted in this bus state
NA —Signal is not asserted in this state
X —Don't care
S —Signal was asserted in previous state and remains asserted in this state
— —State N+2 not part of bus cycle
EXAMPLE A:
A system uses a watchdog timer to terminate accesses to an unpopulated address
space. The timer asserts BERR after timeout (case 3).
Table 7-9. STERM, BERR, and HALT Assertion Results
Case
No. Control
Signal Asserted on Rising
Edge of State Result
N N+2
1 STERM
BERR
HALT
A
NA
NA
—
—
—
Normal cycle terminate and continue.
2 STERM
BERR
HALT
NA
NA
A/S
A
NA
S
Normal cycle terminate and halt. Continue when HALT
negated.
3 STERM
BERR
HALT
NA
A/S
NA
A
S
NA
Terminate and take bus error exception, possibly
deferred.
4 STERM
BERR
HALT
A
A
N/A
—
—
—
Terminate and take bus error exception, possibly
deferred.
5 STERM
BERR
HALT
NA
A
A/S
A
S
S
Terminate and retry when HALT negated.
6 STERM
BERR
HALT
A
A
A
—
—
—
Terminate and retry when HALT negated.
Bus Operation
7-84 MC68030 USER’S MANUAL MOTOROLA
EXAMPLE B:
A system uses error detection and correction on RAM contents. The designer may:
1. Delay DSACKx until data is verified; assert BERR and HALT simultaneously to indi-
cate to the processor to automatically retry the error cycle (case 5) or, if data is valid,
assert DSACKx (case 1).
2. Delay DSACKx until data is verified and assert BERR with or without DSACKx if data
is in error (case 3). This initiates exception processing for software handling of the
condition.
3. Return DSACKx prior to data verification. If data is invalid, BERR is asserted on the
next clock cycle (case 4). This initiates exception processing for software handling of
the condition.
4. Return DSACKx prior to data verification; if data is invalid, assert BERR and HALT on
the next clock cycle (case 6). The memory controller can then correct the RAM prior
to or during the automatic retry.
7.5.1 Bus Errors
The bus error signal can be used to abort the bus cycle and the instruction being executed.
BERR takes precedence over DSACKx or STERM provided it meets the timing constraints
described in MC68030EC/D,
MC68030 Electrical Specifications
. If BERR does not meet
these constraints, it may cause unpredictable operation of the MC68030. If BERR remains
asserted into the next bus cycle, it may cause incorrect operation of that cycle.
When the bus error signal is issued to terminate a bus cycle, the MC68030 may enter
exception processing immediately following the bus cycle, or it may defer processing the
exception. The instruction prefetch mechanism requests instruction words from the bus
controller and the instruction cache before it is ready to execute them. If a bus error occurs
on an instruction fetch, the processor does not take the exception until it attempts to use that
instruction word. Should an intervening instruction cause a branch or should a task switch
occur, the bus error exception does not occur.
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-85
The bus error signal is recognized during a bus cycle in any of the following cases:
• DSACKx (or STERM) and HALT are negated and BERR is asserted.
• HALT and BERR are negated and DSACKx is asserted. BERR is then asserted within
one clock cycle (HALT remains negated).
• BERR is asserted and recognized on the next falling clock edge following the rising
clock edge on which STERM is asserted and recognized (HALT remains negated).
When the processor recognizes a bus error condition, it terminates the current bus cycle in
the normal way. Figure 7-49 shows the timing of a bus error for the case in which neither
DSACKx nor STERM is asserted. Figure 7-50 shows the timing for a bus error that is
asserted after DSACKx. Exceptions are taken in both cases. (Refer to 8.1.2 Bus Error
Exception for details of bus error exception processing.) When BERR is asserted during a
read cycle that supplies data to either on-chip cache, the data in the cache is marked invalid.
However, when a write cycle that writes data into the data cache results in an externally
generated bus error, the data in the cache is not marked invalid.
In the second case, where BERR is asserted after DSACKx is asserted, BERR must be
asserted within specification #48 (refer to MC68030EC/D,
MC68030 Electrical
Specifications
) for purely asynchronous operation, or it must be asserted and remain stable
during the sample window, defined by specifications #27A and #47B, around the next falling
edge of the clock after DSACKx is recognized. If BERR is not stable at this time, the
processor may exhibit erratic behavior. BERR has priority over DSACKx. In this case, data
may be present on the bus, but may not be valid. This sequence may be used by systems
that have memory error detection and correction logic and by external cache memories.
The assertion of BERR described in the third case (recognized after STERM) has
requirements similar to those described in the preceding paragraph. BERR must be stable
throughout the sample window for the next falling edge of the clock, as defined by
specifications #27A and #28A. Figure 7-51 shows the timing for this case.
Bus Operation
7-86 MC68030 USER’S MANUAL MOTOROLA
Figure 7-49. Bus Error without DSACKx
BREAKPOINT
ACKNOWLEDGE
BUS ERROR
ASSERTED
READ CYCLE
CLK
A31-A20
A19-A16
A15-A2
FC2-FC0
SIZ1
R/W
ECS
OCS
AS
DS
DSACK0
DBEN
D23-D16
SIZ0
DSACK1
S0 S2 S4 S0 S2 S4 S0 S2
D7-D0
D15-D8
BREAKPOINT NUMBER
WORD
FETCHED
INSTRUCTION
EXECUTION
(0000)
BREAKPOINT ENCODING
A1-A0
HALT
BERR
CPU SPACE
D31 -D24
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-87
A bus error occurring during a burst fill operation is a special case. If a bus error occurs
during the first cycle of a burst, the data is ignored, the entire cache line is marked invalid,
and the burst operation is aborted. If the cycle is for an instruction fetch, a bus error
exception is made pending. This bus error is processed only if the execution unit attempts
to use either of the two words latched during the bus cycle. If the cycle is for a data fetch,
the bus error exception is taken immediately. Refer to Section 11 Instruction Execution
Timing for more information about pipeline operation.
Figure 7-50. Late Bus Error with DSACKx
CLK
A31-A0
FC2-FC0
R/W
ECS
OCS
AS
DS
DSACK0
DBEN
D31-D0
IPL0-IPL2
DSACK1
S0 S2 Sw S4 S0 S2
Sw S4
SIZ1-SIZ0
BERR
HALT
WRITE WITH BUS ERROR ASSERTED INTERNAL
PROCESSING STACK WRITE
Bus Operation
7-88 MC68030 USER’S MANUAL MOTOROLA
When a bus error occurs after the burst mode has been entered (that is, on the second
access or later), the processor terminates the burst operation, and the cache entry
corresponding to that cycle is marked invalid, but the processor does not take an exception
(see Figure 7-52). If the second cycle is for a portion of a misaligned operand fetch, the
processor runs another read cycle for the second portion with CBREQ negated, as shown
in Figure 7-53. If BERR is asserted again, the MC68030 then takes an exception. The
MC68030 supports late bus errors during a burst fill operation; the timing is the same relative
to STERM and the clock as for a late bus error in a normal synchronous cycle.
Figure 7-51. Late Bus Error with STERM — Exception Taken
AS
CLK
A31-A0
FC2-FC0
SIZ1–SIZ0
S0 S2 S3 S0 S2SwSwSw Sw
R/W
ECS
OCS
DS
STERM
DBEN
BERR
D31-D0
HALT
WRITE WITH BUS ERROR ASSERTED INTERNAL
PROCESSING STACK WRITE
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-89
Figure 7-52. Long-Word Operand Request — Late BERR on Third Access
CLK
A31–A4
A3
A2–A0
FC2–FC0
SIZ1–SIZ0
R/W
S0 S2 S4 S6
ECS
OCS
AS
DS
b4–b7 b8–bB
0111 1000 1100
STERM
CIIN
CIOUT
CBREQ
CBACK
D31–D0
DBEN
BERR
HALT LATE BERR ENDS BURST;
NO EXCEPTION TAKEN
VALUE OF A3:A0 INCREMENTED BY THE SYSTEM HARDWARE
Bus Operation
7-90 MC68030 USER’S MANUAL MOTOROLA
Figure 7-53. Long-Word Operand Request — BERR on Second Access
FC2-FC0
R/W
ECS
OCS
CLK
S0 S2 SwS1 Sw Sw Sw SwS4 S5 Sw Sw
AS
DS
STERM
CBREQ
CBACK
D31–D0
DBEN
b4–b7 bC–bF
SwSw SwSw S3
SIZ1–SIZ0
CIIN
CIOUT
Sw Sw S0 S1 S2 S3 S4 S5Sw
A31-A0 A3:A0 = 1000
DSACK1
DSACK0
BERR
HALT
BURST ABORTED
BUS ERROR ASSERTED INTERNAL
PROCESSING
RERUN CYCLE TO GET LAST
3 BYTES OF OPERAND
0111 1000
VALUE OF A3:A0 INCREMENTED BY THE SYSTEM HARDWARE
Bus Operation
MOTOROLA MC68030 USER’S MANUAL 7-91
7.5.2 Retry Operation
When the BERR and HALT signals are both asserted by an external device during a bus
cycle, the processor enters the retry sequence. A delayed retry, similar to the delayed bus
error signal described previously, can also occur, both for synchronous and asynchronous
cycles.
The processor terminates the bus cycle, places the control signals in their inactive state, and
does not begin another bus cycle until the HALT signal is negated by external logic. After a
synchronization delay, the processor retries the previous cycle using the same access
information (address, function code, size, etc.) The BERR signal should be negated before
S2 of the read cycle to ensure correct operation of the retried cycle. Figure 7-54 shows a
retry operation of an asynchronous cycle, and Figure 7-55 shows a retry operation of a
synchronous cycle.
The processor retries any read or write cycle of a read-modify-write operation separately;
RMC remains asserted during the entire retry sequence.
On the initial access of a burst operation, a retry (indicated by the assertion of BERR and
HALT) causes the processor to retry the bus cycle and assert CBREQ again. Figure 7-56
shows a late retry operation that causes an initial burst operation to be repeated. However,
signaling a retry with simultaneous BERR and HALT during the second, third, or fourth cycle
of a burst operation does not cause a retry operation, even if the requested operand is
misaligned. Assertion of BERR and HALT during a subsequent cycle of a burst operation
causes independent BERR and HALT operations. The external bus activity remains halted
until HALT is negated and the processor acts as previously described for the bus error
during a burst operation.
Asserting BR along with BERR and HALT provides a relinquish and retry operation. The
MC68030 does not relinquish the bus during a read-modify-write operation, except during
the first read cycle. Any device that requires the processor to give up the bus and retry a bus
cycle during a read-modify-write cycle must either assert BERR and BR only (HALT must
not be included) or use the single wire arbitration method discussed in 7.7.4 Bus
Arbitration Control. The bus error handler software should examine the read-modify-write
bit in the special status word (refer to 8.2.1 Special Status Word (SSW)) and take the
appropriate action to resolve this type of fault when it occurs.
Bus Operation
7-92 MC68030 USER’S MANUAL MOTOROLA
Figure 7-54. Asynchronous Late Retry
A31-A0
FC2-FC0
R/W
ECS
OCS
CLK
S0 S2 SwS1
AS
DS
D31–D0
Sw
SIZ1–SIZ0
S3 S4 S5 S0 S2 S4
DSACK1
DSACK0
DATA BUS NOT DRIVEN
BERR
HALT
WRITE CYCLE RETRY SIGNALED HALT RETRY CYCLE
Bus Operation
7-93 MC68030 USER’S MANUAL MOTOROLA
7.5.3 Halt Operation
When HALT is asserted and BERR is not asserted, the MC68030 halts external bus activity
at the next bus cycle boundary. HALT by itself does not terminate a bus cycle. Negating and
reasserting HALT in accordance with the correct timing requirements provides a single-step
(bus cycle to bus cycle) operation. The HALT signal affects external bus cycles only; thus,
a program that resides in the instruction cache and performs no data writes (or reads that
miss in the data cache) may continue executing, unaffected by the HALT signal.
Figure 7-55. Synchronous Late Retry
A31-A0
FC2-FC0
R/W
ECS
OCS
CLK
S0 S2
S1
AS
DS
STERM
SIZ1–SIZ0
S3 S0 S1 S2 S3
D31–D0
BERR
HALT
READ CYCLE
RETRY SIGNALED HALT RETRY CYCLE
Bus Operation
7-94 MC68030 USER’S MANUAL MOTOROLA
The single-cycle mode allows the user to proceed through (and debug) external processor
operations, one bus cycle at a time. Figure 7-57 shows the timing requirements for a single-
cycle operation. Since the occurrence of a bus error while HALT is asserted causes a retry
operation, the user must anticipate retry cycles while debugging in the single-cycle mode.
The single-step operation and the software trace capability allow the system debugger to
trace single bus cycles, single instructions, or changes in program flow. These processor
capabilities, along with a software debugging package, give complete debugging flexibility.
Figure 7-56. Late Retry Operation for a Burst
A31-A0
FC2-FC0
R/W
ECS
OCS
CLK
S0 S2
S1
AS
DS
STERM
SIZ1–SIZ0
S3 S0 S1 S2 S3
D31–D0
BERR
HALT
S4
CIIN
CIOUT
CBREQ
CBACK
READ HALT RETRY
Bus Operation
7-95 MC68030 USER’S MANUAL MOTOROLA
Figure 7-57. Halt Operation Timing
CLK
A31-A0
FC2-FC0
R/W
ECS
OCS
AS
DS
DSACK0
DBEN
DSACK1
S0 S2 S0
BERR
HALT
S4 S2
SIZ1/SIZ0
S4
D31-D0
BR
BG
BGACK
READ HALT
(ARBITRATION PERMITTED
WHILE THE CONTROLLER
IS HALTED)
READ
Bus Operation
7-96 MC68030 USER’S MANUAL MOTOROLA
When the processor completes a bus cycle with the HALT signal asserted, the data bus is
placed in the high-impedance state, and bus control signals are driven inactive (not high-
impedance state); the address, function code, size, and read/write signals remain in the
same state. The halt operation has no effect on bus arbitration (refer to 7.7 Bus
Arbitration). When bus arbitration occurs while the MC68030 is halted, the address and
control signals are also placed in the high-impedance state. Once bus mastership is
returned to the MC68030, if HALT is still asserted, the address, function code, size, and
read/write signals are again driven to their previous states. The processor does not service
interrupt requests while it is halted, but it may assert the IPEND signal as appropriate.
7.5.4 Double Bus Fault
When a bus error or an address error occurs during the exception processing sequence for
a previous bus error, a previous address error, or a reset exception, the bus or address error
causes a double bus fault. For example, the processor attempts to stack several words
containing information about the state of the machine while processing a bus error
exception. If a bus error exception occurs during the stacking operation, the second error is
considered a double bus fault. Only an external reset operation can restart a halted
processor. However, bus arbitration can still occur (refer to 7.7 Bus Arbitration).
The MC68030 indicates that a double bus fault condition has occurred by continuously
asserting the STATUS signal until the processor is reset. The processor asserts STATUS
for one, two, or three clock periods to signal other microsequencer status indications. Refer
to Section 12 Applications Information for a description of the interpretation of the
STATUS signal.
A second bus error or address error that occurs after exception processing has completed
(during the execution of the exception handler routine or later) does not cause a double bus
fault. A bus cycle that is retried does not constitute a bus error or contribute to a double bus
fault. The processor continues to retry the same bus cycle as long as the external hardware
requests it.
Bus Operation
7-97 MC68030 USER’S MANUAL MOTOROLA
7.6 BUS SYNCHRONIZATION
The MC68030 overlaps instruction execution; that is, during bus activity for one instruction,
instructions that do not use the external bus can be executed. Due to the independent
operation of the on-chip caches relative to the operation of the bus controller, many
subsequent instructions can be executed, resulting in seemingly nonsequential instruction
execution. When this is not desired and the system depends on sequential execution
following bus activity, the NOP instruction can be used. The NOP instruction forces
instruction and bus synchronization in that it freezes instruction execution until all pending
bus cycles have completed.
An example of the use of the NOP instruction for this purpose is the case of a write operation
of control information to an external register, where the external hardware attempts to
control program execution based on the data that is written with the conditional assertion of
BERR. If the data cache is enabled and the write cycle results in a hit in the data cache, the
cache is updated. That data, in turn, may be used in a subsequent instruction before the
external write cycle completes. Since the MC68030 cannot process the bus error until the
end of the bus cycle, the external hardware has not successfully interrupted program
execution. To prevent a subsequent instruction from executing until the external cycle
completes, a NOP instruction can be inserted after the instruction causing the write. In this
case, bus error exception processing proceeds immediately after the write before
subsequent instructions are executed. This is an irregular situation, and the use of the NOP
instruction for this purpose is not required by most systems.
Note that even in a system with error detection/correction circuitry, the NOP is not required
for this synchronization. Since the MMU always checks the validity of write cycles before
they proceed to the data cache and are executed externally, the MC68030 is guaranteed to
write correct data to the cache. Thus, there is no danger in subsequent instructions using
erroneous data from the cache before an external bus error signals an error.
A bus synchronization example is given in Figure 7-58.
Bus Operation
7-98 MC68030 USER’S MANUAL MOTOROLA
7.7 BUS ARBITRATION
The bus design of the MC68030 provides for a single bus master at any one time: either the
processor or an external device. One or more of the external devices on the bus can have
the capability of becoming bus master. Bus arbitration is the protocol by which an external
device becomes bus master; the bus controller in the MC68030 manages the bus arbitration
signals so that the processor has the lowest priority. External devices that need to obtain the
bus must assert the bus arbitration signals in the sequences described in the following
paragraphs. Systems having several devices that can become bus master require external
circuitry to assign priorities to the device so that, when two or more external devices attempt
to become bus master at the same time, the one having the highest priority becomes bus
master first. The sequence of the protocol is:
1. An external device asserts the bus request signal.
2. The processor asserts the bus grant signal to indicate that the bus will become avail-
able at the end of the current bus cycle.
3. The external device asserts the bus grant acknowledge signal to indicate that it has
assumed bus mastership.
BR may be issued any time during a bus cycle or between cycles. BG is asserted in
response to BR; it is usually asserted as soon as BR has been synchronized and
recognized, except when the MC68030 has made an internal decision to execute a bus
cycle. Then, the assertion of BG is deferred until the bus cycle has begun. Additionally, BG
is not asserted until the end of a read-modify-write operation (when RMC is negated) in
response to a BR signal. When the requesting device receives BG and more than one
external device can be bus master, the requesting device should begin whatever arbitration
is required. The external device asserts BGACK when it assumes bus mastership and
Figure 7-58. Bus Synchronization Example
S0 Sw
EXTERNAL WRITE
WRITE TO D. CACHE D. CACHE READ
MOVE. L D0, (A0)
NOP PREVENTS EXECUTION OF SUBSEQUENT
INSTRUCTIONS UNTIL MOVE. L D0, (A0)
WRITE CYCLE COMPLETES
MOVE . L (A0), D1
Bus Operation
7-99 MC68030 USER’S MANUAL MOTOROLA
maintains BGACK during the entire bus cycle (or cycles) for which it is bus master. The
following conditions must be met for an external device to assume mastership of the bus
through the normal bus arbitration procedure:
• It must have received BG through the arbitration process.
•AS
must be negated, indicating that no bus cycle is in progress, and the external device
must ensure that all appropriate processor signals have been placed in the high-imped-
ance state (by observing specification #7 in MC68030EC/D,
MC68030 Electrical Spec-
ifications
).
• The termination signal (DSACKx or STERM) for the most recent cycle must have be-
come inactive, indicating that external devices are off the bus (optional, refer to 7.7.3
Bus Grant Acknowledge).
• BGACK must be inactive, indicating that no other bus master has claimed ownership
of the bus.
Figure 7-59 is a flowchart showing the detail involved in bus arbitration for a single device.
Figure 7-60 is a timing diagram for the same operation. This technique allows processing of
bus requests during data transfer cycles.
The timing diagram shows that BR is negated at the time that BGACK is asserted. This type
of operation applies to a system consisting of the processor and one device capable of bus
mastership. In a system having a number of devices capable of bus mastership, the bus
request line from each device can be wire-ORed to the processor. In such a system, more
than one bus request can be asserted simultaneously.
The timing diagram in Figure 7-60 shows that BG is negated a few clock cycles after the
transition of the BGACK signal. However, if bus requests are still pending after the negation
of BG, the processor asserts another BG within a few clock cycles after it was negated. This
additional assertion of BG allows external arbitration circuitry to select the next bus master
before the current bus master has finished with the bus. The following paragraphs provide
additional information about the three steps in the arbitration process.
Bus arbitration requests are recognized during normal processing, RESET assertion, HALT
assertion, and even when the processor has halted due to a double bus fault.
Bus Operation
7-100 MC68030 USER’S MANUAL MOTOROLA
7.7.1 Bus Request
External devices capable of becoming bus masters request the bus by asserting BR. This
can be a wire-ORed signal (although it need not be constructed from open-collector devices)
that indicates to the processor that some external device requires control of the bus. The
processor is effectively at a lower bus priority level than the external device and relinquishes
the bus after it has completed the current bus cycle (if one has started).
If no acknowledge is received while the BR is active, the processor remains bus master once
BR is negated. This prevents unnecessary interference with ordinary processing if the
arbitration circuitry inadvertently responds to noise or if an external device determines that
it no longer requires use of the bus before it has been granted mastership.
Figure 7-59. Bus Arbitration Flowchart for Single Request
1) ASSERT BUS GRANT (BG)
GRANT BUS ARBITRATION
TERMINATE ARBITRATION
1) NEGATE BG AND WAIT FOR BGACK TO
BE NEGATED
REARBITRATE OR RESUME
CONTROLLER OPERATION
REQUEST THE BUS
1) ASSERT BUS REQUEST (BR)
REQUESTING DEVICECONTROLLER
ACKNOWLEDGE BUS MASTERSHIP
1) EXTERNAL ARBITRATION DETERMINES
NEXT BUS MASTER
2) NEXT BUS MASTER WAITS FOR
CURRENT CYCLE TO COMPLETE
3) NEXT BUS MASTER ASSERTS BUS
GRANT ACKNOWLEDGE (BGACK) TO
BECOME NEW MASTER
4) BUS MASTER NEGATES BR
OPERATE AS BUS MASTER
RELEASE BUS MASTERSHIP
1) PERFORM DATA TRANSFERS
(READ AND WRITE CYCLES)
1) NEGATE BGACK
Bus Operation
7-101 MC68030 USER’S MANUAL MOTOROLA
7.7.2 Bus Grant
The processor asserts BG as soon as possible after receipt of BR. This is immediately
following internal synchronization except during a read-modify-write cycle or following an
internal decision to execute a bus cycle. During a read-modify-write cycle, the processor
does not assert BG until the entire operation has completed. RMC is asserted to indicate
Figure 7-60. Bus Arbitration Operation Timing
A31-A0
FC2-FC0
ECS
OCS
AS
DS
DSACK1
CLK
S0 S4 S0
SIZ1-SIZ0
R/W
DSACK0
DBEN
S2 S2
BGACK
BG
BR
D31-D0
CONTROLLER DMA DEVICE CONTROLLER
Bus Operation
7-102 MC68030 USER’S MANUAL MOTOROLA
that the bus is locked. In the case an internal decision to execute another bus cycle, BG is
deferred until the bus cycle has begun.
BG may be routed through a daisy-chained network or through a specific priority-encoded
network. The processor allows any type of external arbitration that follows the protocol.
7.7.3 Bus Grant Acknowledge
Upon receiving BG, the requesting device waits until AS, DSACKx (or synchronous
termination, STERM), and BGACK are negated before asserting its own BGACK. The
negation of the AS indicates that the previous master releases the bus after specification #7
(refer to MC68030EC/D,
MC68030 Electrical Specifications
). The negation of DSACKx or
STERM indicates that the previous slave has completed its cycle with the previous master.
Note that in some applications, DSACKx might not be used in this way.
General-purpose devices are then connected to be dependent only on AS. When BGACK
is asserted, the device is the bus master until it negates BGACK. BGACK should not be
negated until all bus cycles required by the alternate bus master are completed. Bus
mastership terminates at the negation of BGACK. The BR from the granted device should
be negated after BGACK is asserted. If a BR is still pending after the assertion of BGACK,
another BG is asserted within a few clocks of the negation of BG, as described in the 7.7.4
Bus Arbitration Control. Note that the processor does not perform any external bus cycles
before it reasserts BG in this case.
7.7.4 Bus Arbitration Control
The bus arbitration control unit in the MC68030 is implemented with a finite state machine.
As discussed previously, all asynchronous inputs to the MC68030 are internally
synchronized in a maximum of two cycles of the processor clock.
As shown in Figure 7-61, input signals labeled R and A are internally synchronized versions
of the BR and BGACK signals, respectively. The BG output is labeled G, and the internal
high-impedance control signal is labeled T. If T is true, the address, data, and control buses
are placed in the high-impedance state after the next rising edge following the negation of
AS and RMC. All signals are shown in positive logic (active high), regardless of their true
active voltage level.
Bus Operation
7-103 MC68030 USER’S MANUAL MOTOROLA
State changes occur on the next rising edge of the clock after the internal signal is valid. The
BG signal transitions on the falling edge of the clock after a state is reached during which G
changes. The bus control signals (controlled by T) are driven by the processor, immediately
following a state change, when bus mastership is returned to the MC68030.
State 0, at the top center of the diagram, in which G and T are both negated, is the state of
the bus arbiter while the processor is bus master. Request R and acknowledge A keep the
arbiter in state 0 as long as they are both negated. When a request R is received, both grant
G and signal T are asserted (in state 1 at the top left). The next clock causes a change to
state 2, at the lower left, in which G and T are held. The bus arbiter remains in that state until
acknowledge A is asserted or request R is negated. Once either occurs, the arbiter changes
to the center state, state 3, and negates grant G. The next clock takes the arbiter to state 4,
at the upper right, in which grant G remains negated and signal T remains asserted. With
acknowledge A asserted, the arbiter remains in state 4 until A is negated or request R is
Figure 7-61. Bus Arbitration State Diagram
RA
RA
XX
RA RA
RA
XX
RX
RA
XA
RA
RX
XA
RA
GT
STATE 1
GT
STATE 0
GT
STATE 4
GT
STATE 5
GT
STATE 6
GT
STATE 2
GT
STATE 3
XX
R - BUS REQUEST
A - BUS GRANT ACKNOWLEDGE
G - BUS GRANT
T - THREE-STATE CONTROL TO BUS CONTROL LOGIC
X - DON'T CARE
NOTE: The BG output will not be asserted while RMC is asserted.
Bus Operation
7-104 MC68030 USER’S MANUAL MOTOROLA
again asserted. When A is negated, the arbiter returns to the original state, state 0, and
negates signal T. This sequence of states follows the normal sequence of signals for
relinquishing the bus to an external bus master. Other states apply to other possible
sequences of combinations of R and A. As shown by the path from state 0 to state 4, BGACK
alone can be used to place the processor's external bus buffers in the high-impedance state,
providing single-wire arbitration capability.
The read-modify-write sequence is normally indivisible to support semaphore operations
and multiprocessor synchronization. During this indivisible sequence, the MC68030 asserts
the RMC signal and causes the bus arbitration state machine to ignore bus requests
(assertions of BR) that occur after the first read cycle of the read-modify-write sequence by
not issuing bus grants (asserting BG).
In some cases, however, it may be necessary to force the MC68030 to release the bus
during an read-modify-write sequence. One way for an alternate bus master to force the
MC68030 to release the bus applies only to the first read cycle of an read-modify-write
sequence. The MC68030 allows normal bus arbitration during this read cycle; a normal
relinquish and retry operation (asserting BERR, HALT, and BR at the same time) is used.
Note that this method applies only to the first read cycle of the read-modify-write sequence,
but this method preserves the integrity of the read-modify-write sequence without imposing
any constraint on the alternate bus master.
A second method is single-wire arbitration, the timing of which is shown in Figure 7-62. An
alternate master forces the MC68030 to release the bus by asserting BGACK and waits for
AS to negate before taking the bus. It applies to all bus cycles of a read-modify-write
sequence, but can cause system integrity problems if used improperly. The alternate bus
master must guarantee the integrity of the read-modify-write sequence by not altering the
contents of memory locations accessed by the read-modify-write sequence. Note that for
the method to operate properly, AS must be observed to be negated (high) on two
consecutive clock edges before the alternate bus master takes the bus. Waiting for this
condition ensures that any current or pending bus activity has completed or has been pre-
empted.
Bus Operation
7-105 MC68030 USER’S MANUAL MOTOROLA
A timing diagram of the bus arbitration sequence during a processor bus cycle is shown in
Figure 7-60. The bus arbitration sequence while the bus is inactive (i.e., executing internal
operations such as a multiply instruction) is shown in Figure 7-63.
7.8 RESET OPERATION
RESET is a bidirectional signal with which an external device resets the system or the
processor resets external devices. When power is applied to the system, external circuitry
should assert RESET for a minimum of 520 clocks after VCC is within tolerance. Figure 7-64
is a timing diagram of the powerup reset operation, showing the relationships between
RESET, VCC, and bus signals. The clock signal is required to be stable by the time VCC
reaches the minimum operating specification. During the reset period, the entire bus three-
states (except for non-three-statable signals, which are driven to their inactive state). Once
RESET negates, all control signals are driven to their inactive state, the data bus is in read
mode, and the address bus is driven. After this, the first bus cycle for reset exception
processing begins.
Figure 7-62. Single-Wire Bus Arbitration Timing Diagram
NOTE: The alternate bus master must sample AS high on two consecutive rising edges of the clock (after BGACK is
recognized low) before taking the bus.
16
7
47A
12
TAKE BUS
SEE NOTE
DO NOT
TAKE BUS
9
12
47A
CLK
AS
BGACK
ADDRESS
Bus Operation
7-106 MC68030 USER’S MANUAL MOTOROLA
The external RESET signal resets the processor and the entire system. Except for the initial
reset, RESET should be asserted for at least 520 clock periods to ensure that the processor
resets. Asserting RESET for 10 clock periods is sufficient for resetting the processor logic;
the additional clock periods prevent a reset instruction from overlapping the external RESET
signal.
Figure 7-63. Bus Arbitration Operation (Bus Inactive)
A31-A0
FC2-FC0
ECS
OCS
AS
DS
DSACK1
CLK S4 S0
SIZ1-SIZ0
R/W
DSACK0
DBEN
BGACK
BG
BR
D31-D0
CONTROLLER CONTROLLERALTERNATE MASTER
BUS INACTIVE
(ARBITRATION PERMITTED
WHILE THE CONTROLLER IS
INACTIVE OR HALTED)
Bus Operation
7-107 MC68030 USER’S MANUAL MOTOROLA
Resetting the processor causes any bus cycle in progress to terminate as if DSACKx,
BERR, or STERM had been asserted. In addition, the processor initializes registers
appropriately for a reset exception. Exception processing for a reset operation is described
in 8.1.1 Reset Exception.
When a reset instruction is executed, the processor drives the RESET signal for 512 clock
cycles. In this case, the processor resets the external devices of the system, and the internal
registers of the processor are unaffected. The external devices connected to the RESET
signal are reset at the completion of the reset instruction. An external RESET signal that is
asserted to the processor during execution of a reset instruction must extend beyond the
reset period of the instruction by at least eight clock cycles to reset the processor. Figure 7-
65 shows the timing information for the reset instruction.
Figure 7-64. Initial Reset Operation Timing
ISP
READ
STARTS
ALL CONTROL SIGNALS
INACTIVE. DATA BUS IN
READ MODE. ADDRESS
BUS DRIVEN
ENTIRE
BUS HIGH
IMPEDANCE
BUS STATE UNKNOWN
t = >520 CLOCKS
1<4 CLOCKS
4 CLOCKS
CLK
+5
VOLTS
VCC
BUS
CYCLES
RESET
Bus Operation
7-108 MC68030 USER’S MANUAL MOTOROLA
Figure 7-65. Processor-Generated Reset Operation
CLK
A31-A0
FC2-FC0
R/W
ECS
OCS
AS
DS
DSACK0
DBEN
SIZ1-SIZ0
DSACK1
HALT
S0 S2S4
D31-D0
S2S0
RESET
READ RESET INTERNAL
512 CLOCKS RESUME NORMAL
OPERATION
