How to Use 25LC1024: Examples, Pinouts, and Specs

The 25LC1024 is a 1 Mbit (128K x 8) serial EEPROM manufactured by Microchip Technology. It is designed for non-volatile data storage, meaning it retains data even when power is removed. The component communicates using the Serial Peripheral Interface (SPI) protocol, making it suitable for a wide range of applications requiring reliable and efficient data storage.

• Data logging in embedded systems
• Configuration and calibration data storage
• Firmware storage for microcontrollers
• Industrial automation systems
• Consumer electronics requiring non-volatile memory

The following table outlines the key technical details of the 25LC1024:

The 25LC1024 is available in an 8-pin package. The pinout and descriptions are as follows:

1. Power Supply: Connect the VCC pin to a stable power source (2.5V to 5.5V) and the VSS pin to ground.
2. SPI Connections:
   • Connect the CS pin to a GPIO pin on the microcontroller to enable/disable the EEPROM.
   • Connect the SCK pin to the SPI clock pin of the microcontroller.
   • Connect the SI pin to the SPI MOSI (Master Out Slave In) pin.
   • Connect the SO pin to the SPI MISO (Master In Slave Out) pin.
3. Optional Pins:
   • Connect the WP pin to VCC if write protection is not required.
   • Connect the HOLD pin to VCC if the hold function is not needed.
4. SPI Configuration: Configure the SPI interface on the microcontroller with the following settings:
   • Clock polarity (CPOL): 0
   • Clock phase (CPHA): 0
   • Data order: MSB first
5. Data Transfer:
   • To write data, send the WRITE instruction (0x02) followed by the memory address and data bytes.
   • To read data, send the READ instruction (0x03) followed by the memory address and read the data bytes.

• Write Protection: Use the WP pin to prevent accidental writes to the memory.
• Timing: Ensure proper timing for SPI signals, especially the clock frequency, to avoid communication errors.
• Pull-Up Resistors: Use pull-up resistors on the CS, WP, and HOLD pins if they are not actively driven.
• Page Writes: The 25LC1024 supports page writes of up to 256 bytes. Ensure that writes do not cross page boundaries.

Below is an example of interfacing the 25LC1024 with an Arduino UNO to write and read data:

#include <SPI.h>

// Pin definitions
const int CS_PIN = 10; // Chip Select pin connected to Arduino pin 10

void setup() {
  // Initialize SPI and Chip Select pin
  SPI.begin();
  pinMode(CS_PIN, OUTPUT);
  digitalWrite(CS_PIN, HIGH); // Set CS pin high to disable the EEPROM
  Serial.begin(9600);
}

void loop() {
  // Example: Write and read a byte of data
  byte addressHigh = 0x00; // High byte of memory address
  byte addressLow = 0x10;  // Low byte of memory address
  byte dataToWrite = 0x55; // Data to write

  // Write data to EEPROM
  writeEEPROM(addressHigh, addressLow, dataToWrite);

  // Read data from EEPROM
  byte dataRead = readEEPROM(addressHigh, addressLow);

  // Print the read data
  Serial.print("Data read from EEPROM: 0x");
  Serial.println(dataRead, HEX);

  delay(1000); // Wait for 1 second
}

void writeEEPROM(byte addressHigh, byte addressLow, byte data) {
  digitalWrite(CS_PIN, LOW); // Enable the EEPROM
  SPI.transfer(0x06);        // Send WREN (Write Enable) command
  digitalWrite(CS_PIN, HIGH); // Disable the EEPROM

  delay(1); // Small delay to ensure WREN is processed

  digitalWrite(CS_PIN, LOW); // Enable the EEPROM
  SPI.transfer(0x02);        // Send WRITE command
  SPI.transfer(addressHigh); // Send high byte of address
  SPI.transfer(addressLow);  // Send low byte of address
  SPI.transfer(data);        // Send data byte
  digitalWrite(CS_PIN, HIGH); // Disable the EEPROM

  delay(5); // Wait for write cycle to complete
}

byte readEEPROM(byte addressHigh, byte addressLow) {
  digitalWrite(CS_PIN, LOW); // Enable the EEPROM
  SPI.transfer(0x03);        // Send READ command
  SPI.transfer(addressHigh); // Send high byte of address
  SPI.transfer(addressLow);  // Send low byte of address
  byte data = SPI.transfer(0x00); // Read data byte
  digitalWrite(CS_PIN, HIGH); // Disable the EEPROM
  return data;
}

1. No Data Read or Write:

   • Ensure the CS pin is properly toggled during SPI communication.
   • Verify the SPI clock frequency is within the supported range (up to 10 MHz at 5V).
   • Check the power supply voltage and connections to the VCC and VSS pins.

2. Corrupted Data:

   • Ensure that write operations do not cross page boundaries.
   • Avoid power interruptions during write cycles.

3. Write Protection Enabled:

   • Verify the state of the WP pin. If it is low, write operations will be disabled.

• Use a logic analyzer or oscilloscope to debug SPI communication if issues persist.
• Double-check the SPI settings (CPOL, CPHA, and data order) in your microcontroller's configuration.
• If using multiple SPI devices, ensure proper handling of the CS pin for each device to avoid conflicts.