Preliminary
This is a product that has fixed target specifications but are subject Ramtron International Corporation
to change pending characterization results. 1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-F-RAM, (719) 481-7000
Rev. 1.1 www.ramtron.com
June 2011 Page 1 of 13
FM25640C
64Kb Serial 5V F-RAM Memory
Features
64K bit Ferroelectric Nonvolatile RAM
Organized as 8,192 x 8 bits
High Endurance 1 Trillion (1012) Read/Writes
36 Year Data Retention at +75C
NoDelay™ Writes
Advanced high-reliability ferroelectric process
Very Fast Serial Peripheral Interface - SPI
Up to 20 MHz maximum bus frequency
Direct hardware replacement for EEPROM
SPI Mode 0 & 3 (CPOL, CPHA=0,0 & 1,1)
Sophisticated Write Protection Scheme
Hardware Protection
Software Protection
Low Power Consumption
250 A Active Current (1 MHz)
4 A (typ.) Standby Current
Industry Standard Configuration
Industrial Temperature -40C to +85C
8-pin “Green”/RoHS SOIC (-G)
Description
The FM25640C is a 64-kilobit nonvolatile memory
employing an advanced ferroelectric process. A
ferroelectric random access memory or F-RAM is
nonvolatile but operates in other respects as a RAM.
It provides reliable data retention for 36 years while
eliminating the complexities, overhead, and system
level reliability problems caused by EEPROM and
other nonvolatile memories.
The FM25640C performs write operations at bus
speed. No write delays are incurred. Data is written to
the memory array immediately after it has been
successfully transferred to the device. The next bus
cycle may commence immediately without the need
for data polling. The FM25640C is capable of
supporting up to 1012 read/write cycles, or a million
times more write cycles than EEPROM.
These capabilities make the FM25640C ideal for
nonvolatile memory applications requiring frequent
or rapid writes. Examples range from data collection,
where the number of write cycles may be critical, to
demanding industrial controls where the long write
time of EEPROM can cause data loss.
The FM25640C provides substantial benefits to users
of serial EEPROM, in a hardware drop-in
replacement. The FM25640C uses the high-speed SPI
bus, which enhances the high-speed write capability
of F-RAM technology. The specifications are
guaranteed over an industrial temperature range of
-40°C to +85°C.
Pin Configuration
Pin Names
Function
/CS
Chip Select
/HOLD
Hold
/WP
Write Protect
SCK
Serial Clock
SI
Serial Data Input
SO
Serial Data Output
VDD
5V
VSS
Ground
Ordering Information
FM25640C-G
“Green”/RoHS 8-pin SOIC
FM25640C-GTR
“Green”/RoHS 8-pin SOIC,
Tape & Reel
CS
SO
WP
VSS
VDD
HOLD
SCK
SI
1
2
3
4
8
7
6
5
FM25640C - 64Kb 5V SPI F-RAM
Rev. 1.1
June 2011 2 of 13
Instruction Decode
Clock Generator
Control Logic
Write Protect
Instruction Register
Address Register
Counter
1,024 x 64
FRAM Array
13
Data I/O Register
8
Nonvolatile Status
Register
3
WP
CS
HOLD
SCK
SO
Figure 1. Block Diagram
Pin Description
Pin Name
Pin Description
/CS
Chip Select: Enables and disables the device. When /CS is high, the output pin SO is hi-
Z, all other inputs are ignored, and the device remains in a low-power standby mode.
When /CS is low, the part will respond to the SCK signal. A falling edge on /CS must
occur for every op-code.
SCK
Serial Clock: All I/O activity is synchronized to the serial clock. Inputs are latched on the
rising edge and outputs occur on the falling edge. The device is static so the clock
frequency may be any value between 0 and 20 MHz and may be interrupted at any time.
/HOLD
Hold: The /HOLD signal is used when the host CPU must interrupt a memory operation
for another task. Asserting the /HOLD signal low pauses the current operation. The
device ignores SCK and /CS. All transitions on /HOLD must occur while SCK is low.
/WP
Write Protect: This pin prevents write operations to the status register. This is critical
since other write protection features are controlled through the status register. A
complete explanation of write protection is provided below. *Note that the function of
/WP is different from the FM25040 where it prevents all writes to the part.
SI
Serial Input: SI is the data input pin. It is sampled on the rising edge of SCK and is
ignored otherwise. It should always be driven to a valid logic level to meet IDD
specifications.
* SI may be connected to SO for a single pin data interface.
SO
Serial Output: SO is the data output pin. It is driven during read cycles and remains hi-Z
at all other times including when HOLD\ is low. Data transitions are driven on the falling
edge of the serial clock.
* SO can be connected to SI for a single pin data interface since the part communicates
in half-duplex.
VDD
Supply Voltage: 5V
VSS
Ground
FM25640C - 64Kb 5V SPI F-RAM
Rev. 1.1
June 2011 3 of 13
Overview
The FM25640C is a serial F-RAM memory. The
memory array is logically organized as 8,192 x 8 and
is accessed using an industry standard Serial
Peripheral Interface or SPI bus. Functional operation
of the F-RAM is similar to serial EEPROMs. The
major difference between the FM25640C and a serial
EEPROM with the same pinout relates to its superior
write performance.
Memory Architecture
When accessing the FM25640C, the user addresses
8,192 locations of 8 data bits each. These data bits
are shifted in and out serially. The addresses are
accessed using the SPI protocol, which includes a
chip select (to permit multiple devices on the bus), an
op-code and a two-byte address. The upper 3 bits of
the address range are ignored by the device. The
complete address of 13-bits specifies each byte
address uniquely.
Most functions of the FM25640C either are
controlled by the SPI interface or are handled
automatically by on-board circuitry. The access time
for memory operation essentially is zero, beyond the
time needed for the serial protocol. That is, the
memory is read or written at the speed of the SPI bus.
Unlike an EEPROM, it is not necessary to poll the
device for a ready condition since writes occur at bus
speed. That is, by the time a new bus transaction can
be shifted into the part, a write operation will be
complete. This is explained in more detail in the
interface section.
Users expect several obvious system benefits from
the FM25640C due to its fast write cycle and high
endurance as compared with EEPROM. However
there are less obvious benefits as well. For example
in a high noise environment, the fast-write operation
is less susceptible to corruption than an EEPROM
since it is completed quickly. By contrast, an
EEPROM requiring milliseconds to write is
vulnerable to noise during much of the cycle.
Note that the FM25640C contains no power
management circuits other than a simple internal
power-on reset. It is the user’s responsibility to
ensure that VDD is within datasheet tolerances to
prevent incorrect operation. It is recommended
that the part is not powered down with chip
enable active.
Serial Peripheral Interface – SPI Bus
The FM25640C employs a Serial Peripheral Interface
(SPI) bus. It is specified to operate at speeds up to 20
MHz. This high-speed serial bus provides high
performance serial communication to a host
microcontroller. Many common microcontrollers
have hardware SPI ports allowing a direct interface.
It is quite simple to emulate the port using ordinary
port pins for microcontrollers that do not. The
FM25640C operates in SPI Mode 0 and 3.
The SPI interface uses a total of four pins: clock,
data-in, data-out, and chip select. It is possible to
connect the two data lines together. Figure 2
illustrates a typical system configuration using the
FM25640C with a microcontroller that offers an SPI
port. Figure 3 shows a similar configuration for a
microcontroller that has no hardware support for the
SPI bus.
Protocol Overview
The SPI interface is a synchronous serial interface
using clock and data lines. It is intended to support
multiple devices on the bus. Each device is activated
using a chip select. Once chip select is activated by
the bus master, the FM25640C will begin monitoring
the clock and data lines. The relationship between the
falling edge of /CS, the clock, and data is dictated by
the SPI mode. The device will make a determination
of the SPI mode on the falling edge of each chip
select. While there are four such modes, the
FM25640C supports modes 0 and 3. Figure 4 shows
the required signal relationships for modes 0 and 3.
In both cases, data is clocked into the FM25640C on
the rising edge of SCK and data is expected on the
first rising edge after /CS goes active. If the clock
begins from a high state, it will fall prior to beginning
data transfer in order to create the first rising edge.
The FM25640C is controlled by SPI op-codes. These
op-codes specify the commands to the part. After /CS
is asserted, the first byte transferred from the bus
master is the op-code. Following the op-code,
addresses and data are then transferred. Note that the
WREN and WRDI op-codes are commands with no
subsequent data transfer.
Important: The /CS must go inactive after an
operation is complete and before a new op-code
can be issued. There is one valid op-code only per
active chip select.
FM25640C - 64Kb 5V SPI F-RAM
Rev. 1.1
June 2011 4 of 13
FM25640C
MOSI: Master Out, Slave In
MISO: Master In, Slave Out
SS: Slave Select
SO SI SCK
CS HOLD
FM25640C
SO SI SCK
CS HOLD
SPI
Microcontroller
SS1
SS2
HOLD1
HOLD2
MISO
MOSI
SCK
Figure 2. System Configuration with SPI port
Microcontroller
FM25640C
SO SI SCK
CS HOLD
Figure 3. System Configuration without SPI port
SPI Mode 0: CPOL=0, CPHA=0
01234567
SPI Mode 3: CPOL=1, CPHA=1
01234567
Figure 4. SPI Modes 0 & 3
FM25640C - 64Kb 5V SPI F-RAM
Rev. 1.1
June 2011 5 of 13
Data Transfer
All data transfers to and from the FM25640C occur
in 8-bit groups. They are synchronized to the clock
signal (SCK) and they transfer most significant bit
(MSB) first. Serial inputs are registered on the rising
edge of SCK. The SO output is driven from the
falling edge of SCK.
Command Structure
There are six commands called op-codes that can be
issued by the bus master to the FM25640C. They are
listed in the table below. These op-codes control the
functions performed by the memory. They can be
divided into three categories. First, there are
commands that have no subsequent operations. They
perform a single function such as to enable a write
operation. Second are commands followed by one
byte, either in or out. They operate on the status
register. The third group includes commands for
memory transactions followed by an address and one
or more bytes of data.
Table 1. Op-code Commands
Name
Description
Op-code value
WREN
Set Write Enable Latch
0000_0110b
WRDI
Write Disable
0000_0100b
RDSR
Read Status Register
0000_0101b
WRSR
Write Status Register
0000_0001b
READ
Read Memory Data
0000_0011b
WRITE
Write Memory Data
0000_0010b
WREN - Set Write Enable Latch
The FM25640C will power up with writes disabled.
The WREN command must be issued prior to any
write operation. Sending the WREN op-code will
allow the user to issue subsequent op-codes for
write operations. These include writing the status
register and writing the memory.
Sending the WREN op-code causes the internal
Write Enable Latch to be set. A flag bit in the status
register, called WEL, indicates the state of the latch.
WEL=1 indicates that writes are permitted.
Attempting to write the WEL bit in the status
register has no effect. Completing any write
operation will automatically clear the write-enable
latch and prevent further writes without another
WREN command. Figure 5 illustrates the WREN
command bus configuration.
WRDI - Write Disable
The WRDI command disables all write activity by
clearing the Write Enable Latch. The user can verify
that writes are disabled by reading the WEL bit in
the status register and verifying that WEL=0. Figure
6 illustrates the WRDI command bus configuration.
Figure 5. WREN Bus Configuration
Figure 6. WRDI Bus Configuration
FM25640C - 64Kb 5V SPI F-RAM
Rev. 1.1
June 2011 6 of 13
RDSR - Read Status Register
The RDSR command allows the bus master to verify
the contents of the Status register. Reading Status
provides information about the current state of the
write protection features. Following the RDSR op-
code, the FM25640C will return one byte with the
contents of the Status register. The Status register is
described in detail below.
WRSR – Write Status Register
The WRSR command allows the user to select
certain write protection features by writing a byte to
the Status register. Prior to issuing a WRSR
command, the /WP pin must be high or inactive. Note
that on the FM25640C, /WP only prevents writing to
the Status register, not the memory array. Prior to
sending the WRSR command, the user must send a
WREN command to enable writes. Note that
executing a WRSR command is a write operation and
therefore clears the Write Enable Latch. The bus
configuration of RDSR and WRSR in the timing
diagrams below.
Figure 7. RDSR Bus Configuration
Figure 8. WRSR Bus Configuration
Status Register & Write Protection
The write protection features of the FM25640C are
multi-tiered. First, a WREN op-code must be issued
prior to any write operation. Assuming that writes are
enabled using WREN, writes to memory are
controlled by the Status register. As described above,
writes to the status register are performed using the
WRSR command and subject to the /WP pin. The
Status Register is organized as follows.
Table 2. Status Register
Bit
7
6
5
4
3
2
1
0
Name
WPEN
0
0
0
BP1
BP0
WEL
0
Bits 0 and 4-6 are fixed at 0 and cannot be modified.
Note that bit 0 (Ready in EEPROMs) is unnecessary
as the F-RAM writes in real-time and is never busy.
The WPEN, BP1 and BP0 control write protection
features. They are nonvolatile (shaded yellow). The
WEL flag indicates the state of the Write Enable
Latch. This bit is internally set by the WREN
command and is cleared by terminating a write cycle
(/CS high) or by using the WRDI command.
BP1 and BP0 are memory block write protection bits.
They specify portions of memory that are write-
protected as shown in the following table.
Table 3. Block Memory Write Protection
BP1
BP0
Protected Address Range
0
0
None
0
1
1800h to 1FFFh (upper ¼)
1
0
1000h to 1FFFh (upper ½)
1
1
0000h to 1FFFh (all)
FM25640C - 64Kb 5V SPI F-RAM
Rev. 1.1
June 2011 7 of 13
The BP1 and BP0 bits and the Write Enable Latch
are the only mechanisms that protect the memory
from writes. The remaining write protection features
protect inadvertent changes to the block protect bits.
The WPEN bit controls the effect of the hardware
/WP pin. When WPEN is low, the /WP pin is
ignored. When WPEN is high, the /WP pin controls
write access to the status register. Thus the Status
register is write protected if WPEN=1 and /WP=0.
This scheme provides a write protection mechanism,
which can prevent software from writing the memory
under any circumstances. This occurs if the BP1 and
BP0 are set to 1, the WPEN bit is set to 1, and /WP is
set to 0. This occurs because the block protect bits
prevent writing memory and the /WP signal in
hardware prevents altering the block protect bits (if
WPEN is high). Therefore in this condition, hardware
must be involved in allowing a write operation. The
following table summarizes the write protection
conditions.
Table 4. Write Protection
WEL
WPEN
/WP
Protected Blocks
Unprotected Blocks
Status Register
0
X
X
Protected
Protected
Protected
1
0
X
Protected
Unprotected
Unprotected
1
1
0
Protected
Unprotected
Protected
1
1
1
Protected
Unprotected
Unprotected
Memory Operation
The SPI interface, with its relatively high maximum
clock frequency, highlights the fast write capability
of the F-RAM technology. Unlike SPI-bus
EEPROMs, the FM25640C can perform sequential
writes at bus speed. No page register is needed and
any number of sequential writes may be performed.
Write Operation
All writes to the memory array begin with a WREN
op-code. The next op-code is the WRITE instruction.
This op-code is followed by a two-byte address
value. The upper 3-bits of the address are ignored. In
total, the 13-bits specify the address of the first byte
of the write operation. Subsequent bytes are data and
they are written sequentially. Addresses are
incremented internally as long as the bus master
continues to issue clocks. If the last address of 1FFFh
is reached, the counter will roll over to 0000h. Data is
written MSB first.
Unlike EEPROMs, any number of bytes can be
written sequentially and each byte is written to
memory immediately after it is clocked in (after the
8th clock). The rising edge of /CS terminates a
WRITE op-code operation.
Read Operation
After the falling edge of /CS, the bus master can issue
a READ op-code. Following this instruction is a two-
byte address value. The upper 3-bits of the address
are ignored. In total, the 13-bits specify the address of
the first byte of the read operation. After the op-code
and address are complete, the SI line is ignored. The
bus master issues 8 clocks, with one bit read out for
each. Addresses are incremented internally as long as
the bus master continues to issue clocks. If the last
address of 1FFFh is reached, the counter will roll
over to 0000h. Data is read MSB first. The rising
edge of /CS terminates a READ op-code operation.
The bus configuration for read and write operations is
shown below.
Hold
The /HOLD pin can be used to interrupt a serial
operation without aborting it. If the bus master pulls
the /HOLD pin low while SCK is low, the current
operation will pause. Taking the /HOLD pin high
while SCK is low will resume an operation. The
transitions of /HOLD must occur while SCK is low,
but the SCK pin can toggle during a hold state.
FM25640C - 64Kb 5V SPI F-RAM
Rev. 1.1
June 2011 8 of 13
0 1 2 3 4 5 6 7 0 1 2 3 4 5 3 4 5 6 7 0 1 2 3 4 5 6 7
op-code
0 0 0 0 0 0 1 0 MSB
13-bit Address
X X X 12 11 10 4 3 2 1 0 7 6 5 4 3 2 1 0
LSB MSB LSB
CS
SCK
SI
SO
Data
Figure 9. Memory Write
01234567012345 3456701234567
op-code
0000001 MSB
13-bit Address
X X X 12 11 10 4 3 2 1 0
7 6 5 4 3 2 1 0
LSB MSB LSB
CS
SCK
SI
SO Data
1
Figure 10. Memory Read
Endurance
Internally, a F-RAM operates with a read and restore
mechanism. Therefore, endurance cycles are applied
for each access: read or write. The F-RAM
architecture is based on an array of rows and
columns. Each access causes a cycle for an entire
row. In the FM25640C, a row is 64 bits wide. Every
8-byte boundary marks the beginning of a new row.
Endurance can be optimized by ensuring frequently
accessed data is located in different rows.
Regardless, F-RAM read and write endurance is
effectively unlimited at the 20MHz clock speed.
Even at 2000 accesses per second to the same row, 15
years time will elapse before 1012 endurance cycles
occur.
FM25640C - 64Kb 5V SPI F-RAM
Rev. 1.1
June 2011 9 of 13
Electrical Specifications
Absolute Maximum Ratings
Symbol
Description
Ratings
VDD
Power Supply Voltage with respect to VSS
-1.0V to +7.0V
VIN
Voltage on any pin with respect to VSS
-1.0V to +7.0V
and VIN < VDD+1.0V
TSTG
Storage Temperature
-55C to + 125C
TLEAD
Lead Temperature (Soldering, 10 seconds)
260 C
VESD
Electrostatic Discharge Voltage
- Human Body Model (AEC-Q100-002 Rev. E)
- Charged Device Model (AEC-Q100-011 Rev. B)
- Machine Model (AEC-Q100-003 Rev. E)
4.5kV
1.25kV
300V
Package Moisture Sensitivity Level
MSL-1
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating
only, and the functional operation of the device at these or any other conditions above those listed in the operational section of this
specification is not implied. Exposure to absolute maximum ratings conditions for extended periods may affect device reliability.
DC Operating Conditions (TA = -40 C to + 85 C, VDD = 4.5V to 5.5V unless otherwise specified)
Symbol
Parameter
Min
Typ
Max
Units
Notes
VDD
Power Supply Voltage
4.5
5.0
5.5
V
IDD
VDD Supply Current
@ SCK = 1.0 MHz
@ SCK = 20.0 MHz
0.25
4.0
mA
mA
1
ISB
Standby Current
4
10
A
2
ILI
Input Leakage Current
1
A
3
ILO
Output Leakage Current
1
A
3
VIL
Input Low Voltage
-0.3
0.3 VDD
V
VIH
Input High Voltage
0.7 VDD
VDD + 0.3
V
VOL
Output Low Voltage
@ IOL = 2 mA
0.4
V
VOH
Output High Voltage
@ IOH = -2 mA
VDD – 0.8
V
VHYS
Input Hysteresis
0.05 VDD
V
4
Notes
1. SCK toggling between VDD-0.3V and VSS, other inputs VSS or VDD-0.3V
2. SCK = SI = /CS=VDD. All inputs VSS or VDD.
3. VIN or VOUT = VSS to VDD.
4. This parameter is characterized but not 100% tested. Applies only to /CS and SCK pins.
FM25640C - 64Kb 5V SPI F-RAM
Rev. 1.1
June 2011 10 of 13
AC Parameters (TA = -40 C to + 85 C, VDD = 4.5V to 5.5V unless otherwise specified)
Symbol
Parameter
Min
Max
Units
Notes
fCK
SCK Clock Frequency
0
20
MHz
tCH
Clock High Time
22
ns
tCL
Clock Low Time
22
ns
tCSU
Chip Select Setup
10
ns
tCSH
Chip Select Hold
10
ns
tOD
Output Disable
20
ns
2
tODV
Output Data Valid
20
ns
3
tOH
Output Data Hold
0
ns
tD
Deselect Time
60
ns
tR
Data In Rise Time
50
ns
1,2
tF
Data In Fall Time
50
ns
1,2
tH
Data In Hold Time
5
ns
tSU
Data In Setup Time
5
ns
tHS
/HOLD Input Setup Time
10
ns
tHH
/HOLD Input Hold Time
10
ns
tHZ
/HOLD Low to Data Out Hi-Z
20
ns
2
tLZ
/HOLD High to Data Out Lo-Z
20
ns
2
Notes
1. Rise and fall times measured between 10% and 90% of waveform.
2. This parameter is characterized but not 100% tested.
3. For Clock High Time tCH ≤ 100 ns, the parameter tODV is extended such that tCH + tODV ≤ 160 ns.
Capacitance (TA = 25 C, f=1.0 MHz, VDD = 5V)
Symbol
Parameter
Max
Units
Notes
CO
Output Capacitance (SO)
8
pF
1
CI
Input Capacitance
6
pF
1
Notes
1. This parameter is characterized and not 100% tested.
AC Test Conditions
Input Pulse Levels 10% and 90% of VDD
Input rise and fall times 10 ns
Input and output timing levels 0.5 VDD
Output Load Capacitance 100 pF
Data Retention
Symbol
Parameter
Min
Max
Units
Notes
TDR
@ +85ºC
10
-
Years
@ +80ºC
18
-
Years
@ +75ºC
36
-
Years
FM25640C - 64Kb 5V SPI F-RAM
Rev. 1.1
June 2011 11 of 13
Serial Data Bus Timing
CS
SCK
SI
SO
1/tCK tCL tCH tCSH
tODV tOH tOD
tCSU
tSU tH
tD
tRtF
/Hold Timing
CS
SCK
SO
HOLD tHS
tHH
tHZ tLZ
tHS
tHH
Power Cycle Timing
VDD min
tPU
VDD
CS
tVR
tPD
tVF
Power Cycle Timing (TA = -40 C to + 85 C, VDD = 4.5V to 5.5V unless otherwise specified)
Symbol
Parameter
Min
Max
Units
Notes
tPU
VDD(min) to First Access Start
1
ms
tPD
Last Access Complete to VDD(min)
0
s
tVR
VDD Rise Time
30
s/V
1
tVF
VDD Fall Time
100
s/V
1
Notes
1. Slope measured at any point on VDD waveform.
FM25640C - 64Kb 5V SPI F-RAM
Rev. 1.1
June 2011 12 of 13
Mechanical Drawing
(8-pin SOIC – JEDEC MS-012, Variation AA)
Pin 1
3.90 ±0.10 6.00 ±0.20
4.90 ±0.10
0.10
0.25
1.35
1.75
0.33
0.51
1.27 0.10 mm
0.25
0.50 45
0.40
1.27
0.19
0.25
0- 8
Recommended PCB Footprint
7.70
0.65
1.27
2.00
3.70
Refer to JEDEC MS-012 for complete dimensions and notes.
All dimensions in millimeters.
SOIC Package Marking Scheme
Legend:
XXXXXXX= part number, P= package type (G=SOIC)
R=rev code, LLLLLLL= lot code
RIC=Ramtron Int’l Corp, YY=year, WW=work week
Example: FM25640C, “Green” SOIC package, Year 2010, Work Week 51
FM25640C-G
A00002G1
RIC1051
XXXXXXX-P
RLLLLLLL
RICYYWW
FM25640C - 64Kb 5V SPI F-RAM
Rev. 1.1
June 2011 13 of 13
Revision History
Revision
Date
Summary
1.0
3/22/2011
Initial Release
1.1
6/30/2011
Added ESD ratings.