Am28F010 7
BASIC PRINCIPLES
The Am28F010 uses 100% TTL-level control inputs
to manage the command register. Erase and repro-
gramming operations use a fixed 12.0 V
±
5% high
voltage input.
Read Only Memory
Without high V
PP
voltage, the Am28F010 functions as
a read only memory and operates like a standard
EPROM. The control inputs still manage traditional
read, standby, output disable, and Auto select modes.
Command Register
The command register is enabled only when high volt-
age is applied to the V
PP
pin. The erase and repro-
gramming operations are only accessed via the
register. In addition, two-cycle commands are required
for erase and reprogramming operations. The tradi-
tional read, standby, output disable, and Auto select
modes are available via the register.
The Am28F010’s command register is written using
standard microprocessor write timings. The register
controls an internal state machine that manages all de-
vice operations. For system design simplification, the
Am28F010 is designed to support either WE or CE
controlled writes. During a system write cycle, ad-
dresses are latched on the falling edge of WE or CE
whichever occurs last. Data is latched on the rising
edge of WE or CE whichever occur first. To simplify the
following discussion, the WE pin is used as the write
cycle control pin throughout the rest of this text. All
setup and hold times are with respect to the WE signal.
Overview of Erase/Program Operations
Flasherase
Sequence
A multiple step command sequence is required to
erase the Flash device (a two-cycle Erase command
and repeated one cycle verify commands).
Note:
The Flash memory array must be completely
programmed to 0’s prior to erasure. Refer to the
Flashrite
Programming Algorithm.
1.
Erase Setup:
Write the Setup Erase command to
the command register.
2.
Erase:
Write the Erase command (same as Setup
Erase command) to the command register again.
The second command initiates the erase operation.
The system software routines must now time-out
the erase pulse width (10 ms) prior to issuing the
Erase-verify command. An integrated stop timer
prevents any possibility of overerasure.
3.
Erase-Verify:
Write the Erase-verify command to
the command register. This command terminates
the erase operation. After the erase operation,
each byte of the arr ay must be verified. Address in-
formation must be supplied with the Erase-verify
command. This command verifies the margin and
outputs the addressed byte in order to compare the
array data with FFH data (Byte erased).
After successful data verification the Erase-verify
command is written again with new address infor-
mation. Each byte of the array is sequentially veri-
fied in this manner.
If data of the addressed location is not verified, the
Erase sequence is repeated until the entire array is
successfully verified or the sequence is repeated
1000 times.
Flashrite
Programming Sequence
A three step command sequence (a two-cycle Progr am
command and one cycle Verify command) is required
to program a b yte of the Flash arra y. Refer to the Flash-
rite
Algorithm.
1.
Program Setup:
Write the Setup Program com-
mand to the command register.
2.
Program:
Write the Progr am command to the com-
mand register with the appropriate Address and
Data. The system software routines must no w time-
out the program pulse width (10
µ
s) prior to issuing
the Program-verify command. An integrated stop
timer prevents any possibility of overprogramming.
3.
Program-Verify: Write the Program-verify com-
mand to the command register. This command ter-
minates the programming operation. In addition,
this command verifies the margin and outputs the
byte just prog rammed in order to compare the arra y
data with the original data programmed. After suc-
cessful data verification, the programming se-
quence is initiated again f or the next byte address to
be programmed.
If data is not verified successfully, the Program se-
quence is repeated until a successful comparison is
verified or the sequence is repeated 25 times.
Data Protection
The Am28F010 is designed to offer protection against
accidental erasure or programming caused by spurious
system le vel signals that ma y e xist during power transi-
tions. The Am28F010 powers up in its read only state.
Also, with its control register architecture, alteration of
the memory contents only occurs after successful com-
pletion of specific command sequences.
The device also incorporates several features to pre-
vent inadvertent write cycles resulting fromVCC po wer-
up and power-down transitions or system noise.
Low VCC Write Inhibit
To a void initiation of a write cycle during VCC pow er-up
and power-do wn, the Am28F010 loc ks out write cycles
for VCC < VLKO (see DC Characteristics section for
voltages). When VCC < VLKO, the command register is