Fremont Micro Devices
24C256A
Two-Wire Serial EEPROM
256K (8-bit wide)
FEATURES
Low voltage and low power operations:
FT24C256A:
V
CC
= 1.8V to 5.5V
Maximum Standby current < 1µA .
64 bytes page write mode.
Partial page write operation allowed.
Internally organized: 32,768 ×8 (256K).
Standard 2-wire bi-directional serial interface.
Schmitt trigger, filtered inputs for noise protection.
Self-timed write cycle (5ms maximum).
1 MHz (2.5V-5V), 400 kHz (1.8V) Compatibility.
Automatic erase before write operation.
Write protect pin for hardware data protection.
High reliability: typically 1,000,000 cycles endurance.
100 years data retention.
Industrial temperature range (-40℃ to 85℃).
DESCRIPTION
The FT24C256A series are 262,144 bits of serial Electrical Erasable and Programmable Read Only Memory,
commonly known as EEPROM. They are organized as 32,768 words of 8 bits (one byte) each. The devices
are fabricated with proprietary advanced CMOS process for low power and low voltage applications. These
devices are available in standard 8-lead DIP, 8-lead SOP, 8-lead MSOP,8-lead TSSOP and 8-lead UDFN
packages. A standard 2-wire serial interface is used to address all read and write functions. Our extended
V
CC
range (1.8V to 5.5V) devices enables wide spectrum of applications.
PIN CONFIGURATION
FM
Pin Name
A2, A1, A0
SDA
SCL
WP
NC
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Device Address Inputs
Serial Data Input / Open Drain Output
Serial Clock Input
Write Protect
No-Connect
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Pin Function
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Standard 8-lead DIP/SOP/MSOP/TSSOP/UDFN Pb-free packages.
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All these packaging types come in Pb-free certified.
FT24C256A
A0
A1
A2
GND
1
2
3
4
8
7
6
5
24C256A
VCC
WP
SCL
SDA
8L
8L
8L
8L
8L
DIP
SOP
MSOP
TSSOP
UDFN
ABSOLUTE MAXIMUM RATINGS
Industrial operating temperature:
Storage temperature:
Input voltage on any pin relative to ground:
Maximum voltage:
ESD Protection on all pins:
-40℃ to 85℃
-50℃ to 125℃
FM
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* Stresses exceed those listed under “Absolute Maximum Rating” may cause permanent damage to the
device. Functional operation of the device at conditions beyond those listed in the specification is not
guaranteed. Prolonged exposure to extreme conditions may affect device reliability or functionality.
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-0.3V to V
CC
+ 0.3V
8V
>2000V
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24C256A
PIN DESCRIPTIONS
(A) SERIAL CLOCK (SCL)
The rising edge of this SCL input is to latch data into the EEPROM device while the falling edge of this
clock is to clock data out of the EEPROM device.
(B) DEVICE / CHIP SELECT ADDRESSES (A2, A1, A0)
These are the chip select input signals for the serial EEPROM devices. Typically, these signals are
hardwired to either V
IH
or V
IL
. If left unconnected, they are internally recognized as V
IL
.
(C) SERIAL DATA LINE (SDA)
SDA data line is a bi-directional signal for the serial devices. It is an open drain output signal and can be
wired-OR with other open-drain output devices.
(D) WRITE PROTECT (WP)
The FT24C256A devices have a WP pin to protect the whole EEPROM array from programming.
Programming operations are allowed if WP pin is left un-connected or input to V
IL
. Conversely all
programming functions are disabled if WP pin is connected to V
IH
or V
CC
. Read operations is not affected
by the WP pin’s input level.
MEMORY ORGANIZATION
DEVICE OPERATION
(A) SERIAL CLOCK AND DATA TRANSITIONS
(B) START CONDITION
FM
(C) STOP CONDITION
With SCL V
IH
, a SDA transition from low to high is interpreted as a STOP condition. All valid read or
write commands end with a STOP condition. The device goes into the STANDBY mode if it is after a
read command. A STOP condition after page or byte write command will trigger the chip into the
STANDBY mode after the self-timed internal programming finish (see Figure 1).
The 2-wire protocol transmits address and data to and from the EEPROM in 8 bit words. The EEPROM
acknowledges the data or address by outputting a "0" after receiving each word. The ACKNOWLEDGE
th
signal occurs on the 9 serial clock after each word.
(D) ACKNOWLEDGE
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With SCL
V
IH
, a SDA transition from high to low is interpreted as a START condition.
commands must begin with a START condition.
C
The SDA pin is typically pulled to high by an external resistor. Data is allowed to change only when
Serial clock SCL is at V
IL
. Any SDA signal transition may interpret as either a START or STOP condition
as described below.
All valid
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The FT24C256A devices have 512 pages. Since each page has 64 bytes, random word addressing to
FT24C256A will require 15 bits data word addresses.
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24C256A
(E) STANDBY MODE
The EEPROM goes into low power STANDBY mode after a fresh power up, after receiving a STOP bit
in read mode, or after completing a self-time internal programming operation.
Figure 1: Timing diagram for START and STOP conditions
SCL
SDA
START
Condition
Data
Valid
Data
Transition
STOP
Condition
Figure 2: Timing diagram for output ACKNOWLEDGE
START Condition
Data in
C
Data out
O
ACK
FM
DEVICE ADDRESSING
The 2-wire serial bus protocol mandates an 8 bits device address word after a START bit condition to invoke
a valid read or write command. The first four most significant bits of the device address must be 1010,
which is common to all serial EEPROM devices. The next three bits are device address bits. These three
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th
th
device address bits (5 , 6 and 7 ) are to match with the external chip select/address pin states. If a match
th
is made, the EEPROM device outputs an ACKNOWLEDGE signal after the 8 read/write bit, otherwise the
chip will go into STANDBY mode. However, matching may not be needed for some or all device address
th
th
th
bits (5 , 6 and 7 ) as noted below. The last or 8th bit is a read/write command bit. If the 8th bit is at V
IH
then the chip goes into read mode. If a “0” is detected, the device enters programming mode.
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24C256A
WRITE OPERATIONS
(A) BYTE WRITE
A write operation requires two 8-bit data word address following the device address word and
ACKNOWLEDGE signal. Upon receipt of this address, the EEPROM will respond with a “0” and then
clock in the first 8-bit data word. Following receipt of the 8-bit data word, the EEPROM will again output
a “0”. The addressing device, such as a microcontroller, must terminate the write sequence with a
STOP condition. At this time the EEPROM enters into an internally-timed write cycle state. All inputs
are disabled during this write cycle and the EEPROM will not respond until the writing is completed
(figure 3).
(B) PAGE WRITE
A page write is initiated the same way as a byte write, but the microcontroller does not send a STOP
condition after the first data word is clocked in. The microcontroller can transmit up to 63 more data
words after the EEPROM acknowledges receipt of the first data word. The EEPROM will respond with a
“0” after each data word is received. The microcontroller must terminate the page write sequence with a
STOP condition (see Figure 4).
The lower six bits of the data word address are internally incremented following the receipt of each data
word. The higher data word address bits are not incremented, retaining the memory page row location.
If more than 64 data words are transmitted to the EEPROM, the data word address will “roll over” and
the previous data will be overwritten.
(C) ACKNOWLEDGE POLLING
ACKNOWLEDGE polling may be used to poll the programming status during a self-timed internal
programming. By issuing a valid read or write address command, the EEPROM will not acknowledge at
th
the 9 clock cycle if the device is still in the self-timed programming mode. However, if the programming
completes and the chip has returned to the STANDBY mode, the device will return a valid
th
ACKNOWLEDGE signal at the 9 clock cycle.
The 256K EEPROM are capable of 64-byte page write.
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READ OPERATIONS
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The read command is similar to the write command except the 8 read/write bit in address word is set to “1”.
The three read operation modes are described as follows:
The EEPROM internal address word counter maintains the last read or write address plus one if the
power supply to the device has not been cut off. To initiate a current address read operation, the micro-
th
controller issues a START bit and a valid device address word with the read/write bit (8 ) set to “1”. The
th
EEPROM will response with an ACKNOWLEDGE signal on the 9 serial clock cycle. An 8-bit data word
will then be serially clocked out. The internal address word counter will then automatically increase by
th
one. For current address read the micro-controller will not issue an ACKNOWLEDGE signal on the 18
th
clock cycle. The micro-controller issues a valid STOP bit after the 18 clock cycle to terminate the read
operation. The device then returns to STANDBY mode (see Figure 5).
The sequential read is very similar to current address read. The micro-controller issues a START bit
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and a valid device address word with read/write bit (8 ) set to “1”. The EEPROM will response with an
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ACKNOWLEDGE signal on the 9 serial clock cycle. An 8-bit data word will then be serially clocked out.
Meanwhile the internally address word counter will then automatically increase by one.
FM
(B) SEQUENTIAL READ
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(A) CURRENT ADDRESS READ
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