24LC256 / 24AA256 / 24FC256 I²C address

How to set the address

Wire the address pins like this:

A2 A1 A0 → 0x50–0x57

The address pins are pulled low inside the chip: left unconnected, the address is 0x50.

Devices that use the same addresses

Two devices on the same bus can’t answer on the same address. These modules from our list use at least one of these addresses:

If two of them end up on the same address, move one with its address pin, put one behind a TCA9548A multiplexer (0x70–0x77), or use a second I²C bus: the ESP32, ESP32-S3 and RP2040 have two I²C controllers (the ESP32-C3 has one).

Check your whole bus →Add the 24LC256 / 24AA256 / 24FC256 and your other modules: the checker finds conflicts, suggests free addresses and sizes the pull-ups.

7-bit and 8-bit address

I²C addresses are 7 bits long. Some datasheets and libraries write them as 8-bit numbers, with the read/write bit added on the right: that is why the same chip can appear as 0x50 or 0xA0. Arduino’s Wire library and ESPHome use the 7-bit form.

Check that it answers

Upload this sketch with the 24LC256 / 24AA256 / 24FC256 wired to SDA and SCL: it tries every address the chip can use and prints the one that answers. On an ESP32 the default pins are GPIO21 (SDA) and GPIO22 (SCL); on an Arduino Uno, A4 and A5.

#include <Wire.h>

const byte ADDRS[] = {0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57};

void setup() {
  Serial.begin(115200);
  Wire.begin();
  for (byte a : ADDRS) {
    Wire.beginTransmission(a);
    if (Wire.endTransmission() == 0) {
      Serial.print("24LC256 / 24AA256 / 24FC256 answers at 0x");
      if (a < 0x10) Serial.print('0');
      Serial.println(a, HEX);
      return;
    }
  }
  Serial.println("No answer: check the wiring");
}

void loop() {}

In ESPHome the bus is scanned at boot (scan: true is the default): the log lists every address that answers.

i2c:
  sda: GPIO21
  scl: GPIO22
  scan: true

Pull-up resistors

SDA and SCL need pull-up resistors to the supply. Many breakout boards already carry them, often 4.7 kΩ or 10 kΩ, and with several boards on the bus they add up in parallel. The I²C checker works out the allowed range for your bus voltage and speed.

Similar devices

AT24C32 DS1307 DS3231 PCF85063A PCF8523 PCF8563

Addresses checked against the 24LC256 / 24AA256 / 24FC256 datasheet.