How to Use 25LC128: Examples, Pinouts, and Specs

The 25LC128 is a 128 Kbit (16 K 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 SPI (Serial Peripheral Interface) protocol, making it suitable for a wide range of applications requiring reliable and compact memory solutions.

• 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 25LC128:

The 25LC128 is typically available in an 8-pin package. The pinout and descriptions are as follows:

1. Power Supply: Connect the VCC pin to a voltage 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 chip.
   • Connect the SCK, SI, and SO pins to the corresponding SPI pins on the microcontroller.
3. Optional Pins:
   • If write protection is required, connect the WP pin to ground.
   • If the hold function is not used, connect the HOLD pin to VCC.
4. Pull-Up Resistors: Use pull-up resistors on the CS, WP, and HOLD pins if necessary to ensure proper logic levels.

• Write Protection: Enable the write protection feature by pulling the WP pin low to prevent accidental data overwrites.
• Timing Requirements: Ensure the SPI clock frequency does not exceed the maximum specified value (10 MHz at 4.5V to 5.5V).
• Page Write Operations: The 25LC128 supports page write operations with a maximum page size of 64 bytes. Exceeding this limit will overwrite data within the same page.
• Power-Up Timing: Allow sufficient time for the device to power up before initiating communication.

Below is an example of how to interface the 25LC128 with an Arduino UNO using the SPI library:

#include <SPI.h>

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

void setup() {
  // Initialize SPI communication
  SPI.begin();
  
  // Configure the CS pin as output
  pinMode(CS_PIN, OUTPUT);
  digitalWrite(CS_PIN, HIGH); // Set CS pin high (inactive)

  Serial.begin(9600);
  Serial.println("25LC128 EEPROM Initialized");
}

void loop() {
  // Example: Write and read a byte from the EEPROM
  byte address = 0x00; // Memory address to write to
  byte dataToWrite = 0x42; // Data to write (example: 0x42)

  // Write data to EEPROM
  writeEEPROM(address, dataToWrite);

  // Read data back from EEPROM
  byte dataRead = readEEPROM(address);

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

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

void writeEEPROM(byte address, byte data) {
  digitalWrite(CS_PIN, LOW); // Activate the chip
  SPI.transfer(0x02);        // Send WRITE instruction
  SPI.transfer(address);     // Send memory address
  SPI.transfer(data);        // Send data byte
  digitalWrite(CS_PIN, HIGH); // Deactivate the chip
  delay(5);                  // Wait for write cycle to complete
}

byte readEEPROM(byte address) {
  digitalWrite(CS_PIN, LOW); // Activate the chip
  SPI.transfer(0x03);        // Send READ instruction
  SPI.transfer(address);     // Send memory address
  byte data = SPI.transfer(0x00); // Read data byte
  digitalWrite(CS_PIN, HIGH); // Deactivate the chip
  return data;
}

1. No Data Read from EEPROM:

   • Ensure the CS, SCK, SI, and SO pins are correctly connected to the microcontroller.
   • Verify that the SPI clock frequency is within the specified range.

2. Write Operations Not Working:

   • Check if the WP pin is pulled low, which disables write operations.
   • Ensure the write enable (WREN) instruction is sent before attempting to write data.

3. Corrupted Data:

   • Avoid exceeding the 64-byte page size during write operations.
   • Ensure proper power supply stability during read/write operations.

4. Device Not Responding:

   • Verify that the CS pin is being toggled correctly to enable/disable the chip.
   • Check for loose or incorrect wiring.

Q: Can I use the 25LC128 with a 3.3V microcontroller?
A: Yes, the 25LC128 operates within a voltage range of 2.5V to 5.5V, making it compatible with 3.3V systems.

Q: How do I erase data from the EEPROM?
A: Data can be overwritten directly by writing new data to the same address. There is no need for a separate erase operation.

Q: What happens if I exceed the page size during a write operation?
A: If you exceed the 64-byte page size, the data will wrap around and overwrite the beginning of the same page.

Q: How long does the data remain stored in the EEPROM?
A: The 25LC128 has a typical data retention period of 200 years under normal operating conditions.