How to Use 25LC320: Examples, Pinouts, and Specs

The 25LC320 is a 32 Kbit (4K 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 applications requiring fast and reliable data transfer.

• 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 25LC320:

The 25LC320 is typically available in an 8-pin package. The pinout and descriptions are as follows:

1. Power Supply: Connect the VCC pin to a regulated 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 device.
   • 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.

• Ensure the CS pin is pulled high when the device is not in use to avoid unintentional operations.
• Avoid exceeding the maximum clock frequency of 10 MHz to ensure reliable communication.
• Use decoupling capacitors (e.g., 0.1 µF) near the VCC pin to stabilize the power supply.
• If using the WP pin for write protection, ensure it is properly configured to prevent accidental writes.

Below is an example of how to interface the 25LC320 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); // Ensure CS is high (inactive)
  Serial.begin(9600);
}

void loop() {
  // Example: Write and read a byte to/from address 0x0000
  writeEEPROM(0x0000, 0x42); // Write 0x42 to address 0x0000
  delay(10); // Wait for write cycle to complete
  byte data = readEEPROM(0x0000); // Read data from address 0x0000

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

  while (1); // Stop the loop
}

// Function to write a byte to the EEPROM
void writeEEPROM(unsigned int address, byte data) {
  digitalWrite(CS_PIN, LOW); // Select the EEPROM
  SPI.transfer(0x02); // Send WRITE instruction
  SPI.transfer((address >> 8) & 0xFF); // Send high byte of address
  SPI.transfer(address & 0xFF); // Send low byte of address
  SPI.transfer(data); // Send data byte
  digitalWrite(CS_PIN, HIGH); // Deselect the EEPROM
}

// Function to read a byte from the EEPROM
byte readEEPROM(unsigned int address) {
  digitalWrite(CS_PIN, LOW); // Select the EEPROM
  SPI.transfer(0x03); // Send READ instruction
  SPI.transfer((address >> 8) & 0xFF); // Send high byte of address
  SPI.transfer(address & 0xFF); // Send low byte of address
  byte data = SPI.transfer(0x00); // Read data byte
  digitalWrite(CS_PIN, HIGH); // Deselect the EEPROM
  return data;
}

1. No Data Read/Write:

   • Ensure the CS pin is properly toggled (low during communication, high otherwise).
   • Verify SPI connections and ensure the correct pins are used on the microcontroller.
   • Check the power supply voltage (2.5V to 5.5V).

2. Corrupted Data:

   • Avoid exceeding the maximum clock frequency of 10 MHz.
   • Ensure proper grounding and use decoupling capacitors to reduce noise.

3. Write Operations Failing:

   • Verify that the WP pin is not pulled low, as this enables write protection.
   • Ensure sufficient delay (5 ms) after a write operation to allow the write cycle to complete.

Q1: Can I use the 25LC320 with a 3.3V microcontroller?
A1: Yes, the 25LC320 operates within a voltage range of 2.5V to 5.5V, making it compatible with 3.3V systems.

Q2: How do I erase data on the 25LC320?
A2: The 25LC320 does not have a dedicated erase command. Data can be overwritten directly, but ensure the write cycle time is observed.

Q3: What happens if the power is lost during a write operation?
A3: If power is lost during a write, the data being written may be corrupted. Use a stable power supply and consider adding a capacitor to handle brief power interruptions.