Arduino-EEPROM Library

This article details the use of the Arduino EEPROM library.

The Arduino board is equipped with an EEPROM, a non-volatile memory that can retain data even after the power is turned off, and by using the EEPROM library, you can read/write data to/from the EEPROM.

For other Arduino functions and libraries, please refer to the following article.

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EEPROM Library

Read()/EEPROM Read

The Read() function returns 1-byte data from the EEPROM address specified in the parameter.

Write()/EEPROM Write

The Write() function stores the 1-byte data specified by the parameter at the address in the EEPROM specified by the parameter.

length()/Gets the EEPROM memory size

The length() function returns the EEPROM memory size.

Get()/EEPROM Read 2 bytes or more

The Get() function returns 2 or more bytes of data from the EEPROM address specified in the parameter.

Put()/EEPROM Write 2 bytes or more

The Put() function stores 2 bytes or more of data specified by the parameter at the address in the EEPROM specified by the parameter.

Update()/EEPROM Update

The Update() function stores the 1-byte data specified by the parameter at the EEPROM address specified by the parameter; unlike the Write() function, it does not store the data if the original data is the same as the written data.

EEPROM[]/EEPROM Read or Write

EEPROM[] can read or write 1-byte data to a specified address in EEPROM, using a combination of the Read() and Write() functions.

Sample Programs (Sample Sketches)

Read()/EEPROM Read

#include <EEPROM.h>

void setup() {
  Serial.begin(9600);//Initialize serial communication at 9600bps
}

void loop() {
  int value;
  
  value = EEPROM.read(0x000);//Read data at address "0x000", Assign it to "value"

  Serial.print("Address 0x000: ");//Send string "Address 0x000: "
  Serial.println(value);//Send "value", New line

  while(1);//Infinite loop, Program stop
}

The sample program reads data at address "0x000" in EEPROM and displays the data on the serial monitor.

Write()/EEPROM Write

#include <EEPROM.h>

void setup() {
  Serial.begin(9600);//Initialize serial communication at 9600bps
}

void loop() {
  int value;
  
  EEPROM.write(0x000, 59);//Write data "59" at address "0x000"
  value = EEPROM.read(0x000);//Read data at address "0x000", Assign it to "value"
  
  Serial.print("Address 0x000: ");//Send string "Address 0x000: "
  Serial.println(value);//Send "value", New line
  
  while(1);//Infinite loop, Program stop
}

The sample program writes data "59" to address "0x000" in EEPROM, then reads the data at address "0x000" in EEPROM and displays the data on the serial monitor.

length()/Gets the EEPROM memory size

#include <EEPROM.h>

void setup() {
  Serial.begin(9600);//Initialize serial communication at 9600bps
}

void loop() {
  int size;
  
  size = EEPROM.length();//Get EEPROM memory size, Assign to "size"
  
  Serial.print("EEPROM Memory Size: ");//Send string "EEPROM Memory Size: "
  Serial.print(size);//Send "size"
  Serial.println("Byte");//Send string "Byte", New line

  while(1);//Infinite loop, Program stop
}

The sample program gets the memory size of the EEPROM and displays it on the serial monitor.

Get()/EEPROM Read 2 bytes or more

#include <EEPROM.h>

void setup() {
  Serial.begin(9600);//Initialize serial communication at 9600bps
}

void loop() {
  int value;
  
  EEPROM.put(0x000, 511);//Write data "511" from address "0x000"
  EEPROM.get(0x000, value);//Read data at address "0x000", Assign it to "value"
    
  Serial.print("Address 0x000-0x001：");//Send string "Address 0x000-0x001: "
  Serial.println(value);//Send "value", New line
  
  while(1);//Infinite loop, Program stop
}

In the sample program, the put() function writes two or more bytes of data "511" to the address "0x000" in EEPROM, and then the get() function reads two or more bytes of data "511" at the address "0x000" in EEPROM to display the data on the serial monitor.

Put()/EEPROM Write 2 bytes or more

#include <EEPROM.h>

void setup() {
  Serial.begin(9600);//Initialize serial communication at 9600bps
}

void loop() {
  int value_1, value_2;
  
  EEPROM.put(0x000, 511);//Write data "511" from address "0x000"
  value_1 = EEPROM.read(0x000);//Read data at address "0x000", Assign it to "value_1"
  value_2 = EEPROM.read(0x001);//Read data at address "0x001", Assign it to "value_2"
  
  Serial.print("Address 0x000：");//Send string "Address 0x000: "
  Serial.println(value_1);//Send "value_1", New line
  Serial.print("Address 0x001：");//Send string "Address 0x001: "
  Serial.println(value_2);//Send "value_2", New line
  
  while(1);//Infinite loop, Program stop
}

In the sample program, the put() function writes two or more bytes of data "511" to address "0x000" in EEPROM, and then the read() function reads the data at addresses "0x000" and "0x001" in EEPROM and displays the data on the serial monitor.

The data written by the put() function will be 2 bytes of data, so it will be written to addresses "0x000" and "0x001".

Therefore, when we read the data with the read() function, we find that 255 (0xFF) of lower-level data is stored at address "0x000" and 1 (0x01) of upper-level data at address "0x01", and when the two data are combined, the result is 511 (0x01FF).

Update()/EEPROM Update

#include <EEPROM.h>

void setup() {
  Serial.begin(9600);//Initialize serial communication at 9600bps
}

void loop() {
  int value;
  
  EEPROM.update(0x000, 59);//Write data "59" at address "0x000", if the original data is "59", do not write
  value = EEPROM.read(0x000);//Read data at address "0x000", Assign it to "value"
  
  Serial.print("Address 0x000：");//Send string "Address 0x000: "
  Serial.println(value);//Send "value", New line
  
  while(1);//Infinite loop, Program stop
}

The sample program writes data "59" to address "0x000" in EEPROM, then reads the data at address "0x000" in EEPROM and displays the data on the serial monitor.

The difference between the update() and write() functions is that if the original data is the same as the written data, it is not stored. In the case of this sample program, if the data already written is "59", no new writing will be done.

EEPROM[]/EEPROM Read or Write

#include <EEPROM.h>

void setup() {
  Serial.begin(9600);//Initialize serial communication at 9600bps
}

void loop() {
  int value;
  
  EEPROM[0x000] = 59;//Write data "59" at address "0x000"
  value = EEPROM[0x000];//Read data at address "0x000", Assign it to "value"
  
  Serial.print("Address 0x000：");//Send string "Address 0x000: "
  Serial.println(value);//Send "value", New line
  
  while(1);//Infinite loop, Program stop
}

The sample program writes data "59" to address "0x000" in EEPROM, then reads the data at address "0x000" in EEPROM and displays the data on the serial monitor.

EEPROM[] is easy to use because it combines both the Read() and Write() functions to create a more concise program.