How to Use AT24C256 External EEPROM: Examples, Pinouts, and Specs

The AT24C256 External EEPROM by Hiletgo is a non-volatile memory chip that uses the I2C (Inter-Integrated Circuit) protocol for communication. With a storage capacity of 256 kilobits (32 kilobytes), it is ideal for applications that require data retention after power-off, such as storing configuration settings, calibration data, or user preferences. Common use cases include embedded systems, consumer electronics, and IoT devices.

• Memory Size: 256 Kbit (32 Kbyte)
• Interface: I2C (Two-Wire Interface)
• Operating Voltage: 1.7V to 5.5V
• Write Cycle Time: 5 ms (max)
• Endurance: 1 Million Write Cycles
• Data Retention: 100 Years (min)

• Standard Mode (100 kHz)
• Fast Mode (400 kHz)
• Fast Mode Plus (1 MHz)

1. Power Supply: Connect the Vcc pin to a 1.7V to 5.5V power supply and the GND pin to the ground.
2. I2C Connection: Connect the SDA and SCL pins to the I2C data and clock lines, respectively.
3. Address Pins: Configure the A0, A1, and A2 pins to set the device address. These can be connected to GND or Vcc.
4. Write Protection: The WP pin can be connected to Vcc to prevent writing to the EEPROM.

• Use pull-up resistors on the SDA and SCL lines, typically 4.7kΩ to 10kΩ.
• Ensure that the power supply is stable and within the specified voltage range.
• Avoid exposing the EEPROM to temperatures outside the specified operating range.

#include <Wire.h>

// AT24C256 I2C address is 0x50 if all address pins (A0, A1, A2) are connected to GND
#define EEPROM_I2C_ADDRESS 0x50

void setup() {
  Wire.begin(); // Initialize I2C
  Serial.begin(9600); // Start serial communication at 9600 baud
}

void loop() {
  unsigned int address = 0; // EEPROM memory address
  byte dataToWrite = 45; // Data to write to EEPROM

  // Write data to EEPROM
  writeToEEPROM(address, dataToWrite);
  delay(10); // Short delay to ensure the write process is completed

  // Read data from EEPROM
  byte dataRead = readFromEEPROM(address);
  Serial.print("Data read from EEPROM: ");
  Serial.println(dataRead);

  delay(2000); // Wait for 2 seconds before next read/write
}

void writeToEEPROM(unsigned int address, byte data) {
  Wire.beginTransmission(EEPROM_I2C_ADDRESS);
  Wire.write((int)(address >> 8)); // MSB
  Wire.write((int)(address & 0xFF)); // LSB
  Wire.write(data);
  Wire.endTransmission();

  delay(5); // EEPROM write cycle time (max 5ms)
}

byte readFromEEPROM(unsigned int address) {
  byte data = 0xFF; // Data read from EEPROM

  Wire.beginTransmission(EEPROM_I2C_ADDRESS);
  Wire.write((int)(address >> 8)); // MSB
  Wire.write((int)(address & 0xFF)); // LSB
  Wire.endTransmission();

  Wire.requestFrom(EEPROM_I2C_ADDRESS, 1);
  if (Wire.available()) data = Wire.read();

  return data;
}

• Data Not Retained: Ensure the WP pin is not active unless write protection is desired.
• Incorrect Data Read: Verify the I2C address and connections. Check pull-up resistors on SDA and SCL lines.
• No Communication: Confirm that the power supply is within the specified range and that the I2C bus is not busy or stuck.

Q: How do I set the I2C address for the AT24C256? A: The I2C address is determined by the state of the A0, A1, and A2 pins. Connect these pins to GND or Vcc to set the address.

Q: Can I connect multiple AT24C256 devices on the same I2C bus? A: Yes, you can connect up to 8 devices by configuring the A0, A1, and A2 pins with different combinations.

Q: What is the purpose of the WP pin? A: The WP (Write Protect) pin is used to prevent accidental writes to the EEPROM. When connected to Vcc, the device is write-protected.

For further assistance, consult the manufacturer's datasheet and application notes.