What is AT24C256 EEPROM : Pin Configuration & Its Working

In AT24C256 EEPROM, the term “EEPROM” stands for Electrically Erasable Programmable Memory, which is a non-volatile memory type because the data on the IC remains even when the power is switched OFF. It allows you to store the data in the form of bits and retrieve the data even when the power is OFF. The EEPROMs are classified into two types based on their physical location.

They are Internal EEPROM, which is embedded into MCU, and External EEPROM, which is available in the form of Integrated Circuit and can be connected to MCU using serial interface protocol (I2C or SPI). This article gives a brief description of one of the series of external EEPROM ICs, the AT24C256 EEPROM IC.

What is AT24C256 EEPROM?

The AT24C256 EEPROM is an 8-pin, 32 Kbyte Electrically Erasable Programmable Read-Only Memory Integrated Chip, which is used to store the data/information on this chip and remains even when the power is OFF. It works like a pen drive. The information on this IC can either be overwritten or retrieved if required.


These are Serial EEPROM Atmel microchips with the popular AT25 and AT24 series. The AT24 series EEPROM is an I2C EEPROM and the AT25 series EEPROM is an SPI EEPROM IC.

The wide range of operating voltage of AT24C256 EEPROM is from 1.7 Volts to 5.5 Volts, which can be used as an ideal EEPROM in both 3.3 Volts and 5 Volts systems. The storage space of this IC is 32 Kbyte Or 256Kbit and it is possible to cascade 8 similar EEPROM chips for expansion.

The two-wire protocol (IIC/I2C) is used in the working of this IC, which makes it very easy to interfacing with various MCUs with limited no. of pins. It works as an ideal EEPROM in several battery-related applications because the read current of this AT24C256 IC is 40 microAmps.


Pin Configuration/Pin Diagram

The AT24C256 EEPROM is an 8-pin integrated chip with 32 Kbyte memory. The AT24C256 EEPROM pin configuration is shown in the below tabular form. The pin diagram and the AT24C256 IC are shown in the figure below.

Pin Diagram of AT24C256 EEPROM
Pin Diagram of AT24C256 EEPROM

Pin No.

Pin Configuration


1 A0 (Address Input) It is one of the User configured chip select pins and is used while cascading.
2 A1 (Address Input) It is one of the User configured chip select pins and is used while cascading.
3 A2 (Address Input) It is one of the User configured chip select pins and is used while cascading.
4 Ground/Vss It is connected to the ground of the given circuit.
5 SDA (Serial Data) It refers to the serial data pin for I2C communication
6 SCL (Serial Clock It refers to the Serial Clock pin for I2C communication
7 WP (Write Protect) If this pin is connected to the ground (Vss), then the Write is enabled. The Write pin is disabled when it is connected to Vcc
8 VCC It is connected to the power supply given to the circuit.

Circuit Diagram/How to Use

Let’s learn how to use the AT24C256 EEPROM IC with the help of a small example circuit diagram. With the help of the I2C protocol, the AT24C256 EEPROM IC communicates. The circuit diagram of interfacing EEPROM IC with the MCU is shown in the figure below. The supply voltage of 3.3 Volts or 5 Volts is given to the IC and its communication lines are connected as shown in the below circuit diagram.

Interfacing with Microcontroller
Interfacing with Microcontroller

Connect the pin 6 SCK (Serial Clock) to the SCK pin of the microcontroller (MCU) and Pin 5 SDA (Serial Data) to the SDA pin of the microcontroller. The SCK and SDA pins are pulled to a high communication line with the help of 2 pull-up resistors just like I2C communication. This helps to maintain the bus at a high state in idle condition.

The three select pins of this IC are A0, A1, and A2 are used only when more than one EEPROM or I2C device is connected to the same MCU (Microcontroller unit). Otherwise, these address pins are connected directly to the ground. Observe the above circuit diagram, these 3 pins are connected to the GPIO pins because more than one EEPROM IC can be cascaded if necessary.

To improve the data security in this IC, pin 7 of AT24C256 EEPROM, which is a Write Protect Pin, is used. If WP (Write Protect) is low (logic 0), then the data can be erased or written on the EEPROM IC. Otherwise, the data written on the IC remains the same. If the protection of data is not required, then this pin is grounded (0). We can read the data on the EEPROM at any condition regardless of WP pin status.

After successful communication, we can program the MCU to write/read the data to the EEPROM IC by using the values of the right register. Firstly we should specify the address of the location to where the data is to be read/written. This shows the normal process of how the data is read/written byte by byte.

An additional option of Page Write is provided by the equivalent 24LC512 EEPROM IC so that the user can write the data of 126 bytes continuously without mentioning any address of each byte of data.

The process of exchanging the data between the EEPROM IC and the microcontroller is illustrated in the figure below. The entire message/data is divided into the start bit, slave address, read/write a bit, and the acknowledge bit.

The control code can’t be changed by the user because it is hardcoded and always its value will be 1010. The MCU sets the chip select pin’s value. If the chip select pins A0, A1, A2 are set to low, then the device’s resultant address will be 0x50.

Data Exchanging Process
Data Exchanging Process

AT24C256 EEPROM Specifications

The AT24C256 EEPROM specifications or technical characteristics or features are as follows

  • An AT24C256 EEPROM is a 256Kbit integrated chip.
  • Its operation voltage is range is from 1.7 Volts to 5.5 Volts
  • It is used with a Two-wire serial interface (IIC) or I2C interface
  • The size of storage memory is 32Kbytes (256Kbit)
  • The size of the page writer buffer is 128 bytes
  • The period of write cycle and self-timed erase is 5 msec
  • The read current is 40 microAmps
  • The frequency of compatible clock ranges from 400KHz to 1MHz
  • It provides more than 1Million read/write cycles
  • The standby current is 6 microAmps.
  • It is an 8-pin IC available in UDFN, TSSOP, and VFBGA package types.
  • The power consumption is low
  • The data retention is greater than 100 years
  • It is qualified to employe in various applications of automotive
  • It provides factory programming.

Alternative AT24C256 EEPROM

24C04, 25LC040, 25LC1026 and 24C32 are the alternative AT24C256 EEPROM integrated chips while 24LC512 is an equivalent of AT24C256 EEPROM IC

24C04: It is an 8-Pin serial EEPROM IC, which provides 4096 bits memory with an organization of 512 words for every 8 bits. This IC is widely used in various applications where operations with low voltage and low power are necessary.

The equivalents are AT24C256 EEPROM and 24LC512 EEPROM. The alternatives are 24LC1026 EEPROM, 24C32 EEPROM, and 24LC050 EEPROM ICs. Its operating voltage ranges from 1.7 Volts to 3.6 Volts and provides a memory size of 4k Bit.

Where to Use/Applications of AT24C256 EEPROM

The following are the applications of AT24C256 EEPROM

  • This IC is used in audio devices
  • Used in data logging and data analytics
  • Used in storage devices
  • Used in flash memory with less MCU
  • Used in remote storage devices
  • Used in battery-operated applications.

Thus, this is all about an overview of the AT24C257 EEPROM datasheet – Definition, Pin Configuration/Pin Diagram, Circuit Diagram/How to Use, Specifications, Where to Use/Applications. If you want to store the data in Arduino, then this small EEPROM can be used as an external memory module. It connects with Arduino by using an I2C bus or interface and increases the capacity. Since the Arduino that uses the ATmega chip itself has a specific EEPROM memory with few pins. Here is a question for you, “What are the applications of 24C04 EEPROM IC? “