FM24C64
64Kb FRAM Serial Memory
Features
64K bit Ferroelectric Nonvolatile RAM
•
Organized as 8,192 x 8 bits
•
High Endurance 1 Trillion (10
12
) Read/Writes
•
45 Year Data Retention
•
NoDelay™ Writes
•
Advanced High-Reliability Ferroelectric Process
Fast Two-wire Serial Interface
•
Up to 1 MHz maximum bus frequency
•
Direct hardware replacement for EEPROM
•
Supports legacy timing for 100 kHz & 400 kHz
Low Power Operation
•
5V operation
•
150
µA
Active Current (100 kHz)
•
10
µA
Standby Current
Industry Standard Configuration
•
Industrial Temperature -40° C to +85° C
•
8-pin SOIC (-S)
•
“Green” 8-pin SOIC (-G)
Description
The FM24C64 is a 64-kilobit nonvolatile memory
employing an advanced ferroelectric process. A
ferroelectric random access memory or FRAM is
nonvolatile and performs reads and writes like a
RAM. It provides reliable data retention for 45 years
while eliminating the complexities, overhead, and
system level reliability problems caused by
EEPROM and other nonvolatile memories.
The FM24C64 performs write operations at bus
speed. No write delays are incurred. Data is written to
the memory array in the cycle after it has been
successfully transferred to the device. The next bus
cycle may commence immediately. The FM24C64 is
capable of supporting 10
12
read/write cycles, or a
million times more write cycles than EEPROM.
These capabilities make the FM24C64 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
combination of features allows more frequent data
writes with less overhead for the system.
The FM24C64 provides substantial benefits to users
of serial EEPROM, yet these benefits are available in
a hardware drop-in replacement. The FM24C64 is
available in an industry standard 8-pin SOIC package
using a two-wire protocol. The specifications are
guaranteed over an industrial temperature range of
-40°C to +85°C.
Pin Configuration
A0
A1
A2
VSS
1
2
3
4
8
7
6
5
VDD
WP
SCL
SDA
Pin Names
A0-A2
SDA
SCL
WP
VSS
VDD
Function
Device Select Address
Serial Data/address
Serial Clock
Write Protect
Ground
Supply Voltage 5V
Ordering Information
FM24C64-S
FM24C64-G
8-pin SOIC
“Green” 8-pin SOIC
This product conforms to specifications per the terms of the Ramtron
standard warranty. The product has completed Ramtron’s internal
qualification testing and has reached production status.
Rev. 3.0
Mar. 2005
Ramtron International Corporation
1850 Ramtron Drive, Colorado Springs, CO 80921
(800) 545-FRAM, (719) 481-7000
www.ramtron.com
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FM24C64
Counter
Address
Latch
1,024 x 64
FRAM Array
8
SDA
Serial to Parallel
Converter
Data Latch
SCL
WP
A0-A2
Control Logic
Figure 1. FM24C64 Block Diagram
Pin Description
Pin Name
A0-A2
I/O
Input
Pin Description
Address 2-0: These pins are used to select one of up to 8 devices of the same type on
the same two-wire bus. To select the device, the address value on the three pins must
match the corresponding bits contained in the device address.
Serial Data Address: This is a bi-directional pin used to shift serial data and addresses
for the two-wire interface. It employs an open-drain output and is intended to be wire-
OR’d with other devices on the two-wire bus. The input buffer incorporates a Schmitt
trigger for noise immunity and the output driver includes slope control for falling
edges. A pull-up resistor is required.
Serial Clock: The serial clock input for the two-wire interface. Data is clocked out of
the device on the SCL falling edge, and clocked in on the SCL rising edge. The SCL
input also incorporates a Schmitt trigger input for improved noise immunity.
Write Protect: When WP is high, addresses in the upper quadrant of the logical
memory map will be write-protected. Write access is permitted to the lower three-
quarters of the address space. When WP is low, all addresses may be written. This pin
must not be left floating.
Supply Voltage: 5V
Ground
SDA
I/O
SCL
Input
WP
Input
VDD
VSS
Supply
Supply
Rev. 3.0
Mar. 2005
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FM24C64
Overview
The FM24C64 is a serial FRAM memory. The
memory array is logically organized as a 8,192 x 8 bit
memory array and is accessed using an industry
standard two-wire interface. Functional operation of
the FRAM is similar to serial EEPROMs. The major
difference between the FM24C64 and a serial
EEPROM with the same pinout relates to its superior
write performance.
Two-wire Interface
The FM24C64 employs a bi-directional two-wire bus
protocol using few pins and little board space. Figure
2 illustrates a typical system configuration using the
FM24C64 in a microcontroller-based system. The
industry standard two-wire bus is familiar to many
users but is described in this section.
By convention, any device that is sending data onto
the bus is the transmitter while the target device for
this data is the receiver. The device that is controlling
the bus is the master. The master is responsible for
generating the clock signal for all operations. Any
device on the bus that is being controlled is a slave.
The FM24C64 always is a slave device.
The bus protocol is controlled by transition states in
the SDA and SCL signals. There are four conditions:
Start, Stop, Data bit, and Acknowledge. Figure 3
illustrates the signal conditions that specify the four
states. Detailed timing diagrams are shown in the
Electrical Specifications section.
Memory Architecture
When accessing the FM24C64, the user addresses
8,192 locations each with 8 data bits. These data bits
are shifted serially. The 8,192 addresses are accessed
using the two-wire protocol, which includes a slave
address (to distinguish from other non-memory
devices), and an extended 16-bit address. Only the
lower 13 bits are used by the decoder for accessing
the memory. The upper three address bits should be
set to 0 for compatibility with larger devices in the
future.
The memory is read or written at the speed of the
two-wire 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 is complete. This is explained in more
detail in the interface section below.
Users can expect several obvious system benefits
from the FM24C64 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 FM24C64 contains no power
management circuits other than a simple internal
power-on reset. It is the user’s responsibility to
ensure that V
DD
is within datasheet tolerances to
prevent incorrect operation.
VDD
Microcontroller
Rmin = 1.8 KΩ
Rmax = tR/Cbus
SDA
SCL
SDA
SCL
FM24C64
A0 A1 A2
FM24C64
A0 A1 A2
Figure 2. Typical System Configuration
Rev. 3.0
Mar. 2005
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FM24C64
Figure 3. Data Transfer Protocol
Stop Condition
A Stop condition is indicated when the bus master
drives SDA from low to high while the SCL signal is
high. All operations must end with a Stop condition.
If an operation is pending when a stop is asserted, the
operation will be aborted. The master must have
control of SDA (not a memory read) in order to assert
a Stop condition.
Start Condition
A Start condition is indicated when the bus master
drives SDA from high to low while the SCL signal is
high. All read and write transactions begin with a
Start condition. An operation in progress can be
aborted by asserting a Start condition at any time.
Aborting an operation using the Start condition will
ready the FM24C64 for a new operation.
If during operation the power supply drops below the
specified V
DD
minimum, the system should issue a
Start condition prior to performing another operation
Data/Address Transfer
All data transfers (including addresses) take place
while the SCL signal is high. Except under the two
conditions described above, the SDA signal should
not change while SCL is high.
Acknowledge
The Acknowledge takes place after the 8
th
data bit
has been transferred in any transaction. During this
state the transmitter should release the SDA bus to
allow the receiver to drive it. The receiver drives the
SDA signal low to acknowledge receipt of the byte.
If the receiver does not drive SDA low, the condition
is a No-Acknowledge and the operation is aborted.
The receiver could fail to acknowledge for two
distinct reasons. First, if a byte transfer fails, the No-
Acknowledge ends the current operation so that the
device can be addressed again. This allows the last
byte to be recovered in the event of a
communication error. Second and most common,
the receiver does not acknowledge the data to
deliberately end an operation. For example, during a
read operation, the FM24C64 will continue to place
data onto the bus as long as the receiver sends
acknowledges (and clocks). When a read operation
is complete and no more data is needed, the receiver
must not acknowledge the last byte. If the receiver
acknowledges the last byte, this will cause the
FM24C64 to attempt to drive the bus on the next
clock while the master is sending a new command
such as a Stop command.
Slave Address
The first byte that the FM24C64 expects after a start
condition is the slave address. As shown in Figure 4,
the slave address contains the Slave ID (device
type), the device select address bits, and a bit that
specifies if the transaction is a read or a write. Bits
7-4 define the device type and must be set to 1010b
for the FM24C64. These bits allow other types of
function types to reside on the 2-wire bus within an
identical address range. Bits 3-1 are the select bits
which are equivalent to chip select bits. They must
match the corresponding value on the external
address pins to select the device. Up to eight
FM24C64s can reside on the same two-wire bus by
assigning a different address to each. Bit 0 is the
read/write bit. A 1 indicates a read operation, and a
0 indicates a write.
Rev. 3.0
Mar. 2005
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FM24C64
Device
Select
Memory Operation
The FM24C64 is designed to operate in a manner
very similar to other 2-wire interface memory
products. The major differences result from the
higher performance write capability of FRAM
technology. These improvements result in some
differences between the FM24C64 and a similar
configuration EEPROM during writes. The
complete operation for both writes and reads is
explained below.
Write Operation
All writes begin with a device address, then a
memory address. The bus master indicates a write
operation by setting the LSB of the device address
to a 0. After addressing, the bus master sends each
byte of data to the memory and the memory
generates an acknowledge condition. Any number of
sequential bytes may be written. If the end of the
address range is reached internally, the address
counter will wrap from 1FFFh to 0000h.
Unlike other nonvolatile memory technologies,
there is no write delay with FRAM. The entire
memory cycle occurs in less time than a single bus
clock. Therefore, any operation including a read or
write can occur immediately following a write.
Acknowledge polling, a technique used with
EEPROMs to determine if a write is complete is
unnecessary and will always return a ready
condition.
Internally, the actual memory write occurs after the
8
th
data bit is transferred. It will be complete before
the Acknowledge is sent. Therefore, if the user
desires to abort a write without altering the memory
contents, this should be done using a Start or Stop
condition prior to the 8
th
data bit. The FM24C64
uses no page buffering.
Portions of the memory array can be write protected
using the WP pin. Pulling the WP pin high (V
DD
)
will write-protect addresses in the upper quadrant
from 1800h to 1FFFh. The FM24C64 will not
acknowledge data bytes that are written to protected
addresses. In addition, the address counter will not
increment if writes are attempted to these addresses.
Pulling WP low (V
SS
) will deactivate this feature.
WP should not be left floating.
Figures 5 and 6 illustrate both a single-byte write
and multiple-byte write.
Slave
ID
1
7
0
6
1
5
0
4
A2
3
A1 A0 R/W
2
1
0
Figure 4. Slave Address
Addressing Overview
After the FM24C64 (as receiver) acknowledges the
device address, the master can place the memory
address on the bus for a write operation. The address
requires two bytes. The first is the MSB (upper byte).
Since the device uses only 13 address bits, the value
of the upper three bits are don’t care. Following the
MSB is the LSB (lower byte) with the remaining
eight address bits. The address value is latched
internally. Each access causes the latched address
value to be incremented automatically. The current
address is the value that is held in the latch, either a
newly written value or the address following the last
access. The current address will be held as long as
power remains or until a new value is written. Reads
always use the current address. A random read
address can be loaded by beginning a write operation
as explained below.
After transmission of each data byte and just prior to
the acknowledge, the FM24C64 increments the
internal address latch. This allows the next sequential
byte to be accessed with no additional addressing
externally. After the last address (1FFFh) is reached,
the address latch will roll over to 0000h. There is no
limit to the number of bytes that can be accessed with
a single read or write operation.
Data Transfer
After the address information has been transmitted,
data transfer between the bus master and the
FM24C64 can begin. For a read operation, the
FM24C64 will place 8 data bits on the bus then wait
for an Acknowledge from the master. If the
Acknowledge occurs, the FM24C64 will transfer the
next sequential byte. If the Acknowledge is not sent,
the FM24C64 will end the read operation. For a write
operation, the FM24C64 will accept 8 data bits from
the master and then send an Acknowledge. All data
transfer occurs MSB (most significant bit) first.
Rev. 3.0
Mar. 2005
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