The microcontroller on the Arduino and Genuino AVR based board has EEPROM: memory whose values are kept when the board is turned off (like a tiny hard drive). This library enables you to read and write those bytes.
The supported micro-controllers on the various Arduino and Genuino boards have different amounts of EEPROM: 1024 bytes on the ATmega328P, 512 bytes on the ATmega168 and ATmega8, 4 KB (4096 bytes) on the ATmega1280 and ATmega2560. The Arduino and Genuino 101 boards have an emulated EEPROM space of 1024 bytes.
To use this library
1#include <EEPROM.h>To see a list of examples for the EEPROM library, click the link below:
read()Reads a byte from the EEPROM. Locations that have never been written to have the value of 255.
1EEPROM.read(address)address: the location to read from, starting from 0 (int)
the value stored in that location (byte)
1#include <EEPROM.h>2
3int a = 0;4int value;5
6void setup()7{8 Serial.begin(9600);9}10
11void loop()12{13 value = EEPROM.read(a);14
15 Serial.print(a);16 Serial.print("\t");17 Serial.print(value);18 Serial.println();19
20 a = a + 1;21
22 if (a == 512)23 a = 0;24
25 delay(500);26}write()Write a byte to the EEPROM.
1EEPROM.write(address, value)address: the location to write to, starting from 0 (int)
value: the value to write, from 0 to 255 (byte)
none
Note: An EEPROM write takes 3.3 ms to complete. The EEPROM memory has a specified life of 100,000 write/erase cycles, so you may need to be careful about how often you write to it.
1#include <EEPROM.h>2
3void setup()4{5 for (int i = 0; i < 255; i++)6 EEPROM.write(i, i);7}8
9void loop()10{11}update()Write a byte to the EEPROM. The value is written only if differs from the one already saved at the same address.
1EEPROM.update(address, value)address: the location to write to, starting from 0 (int)
value: the value to write, from 0 to 255 (byte)
none
Note: An EEPROM write takes 3.3 ms to complete. The EEPROM memory has a specified life of 100,000 write/erase cycles, so using this function instead of write() can save cycles if the written data does not change often
1#include <EEPROM.h>2
3void setup()4{5 for (int i = 0; i < 255; i++) {6 // this performs as EEPROM.write(i, i)7 EEPROM.update(i, i);8 }9 for (int i = 0; i < 255; i++) {10 // write value "12" to cell 3 only the first time11 // will not write the cell the remaining 254 times12 EEPROM.update(3, 12);13 }14}15
16void loop()17{18}get()Read any data type or object from the EEPROM.
1EEPROM.get(address, data)address: the location to read from, starting from 0 (int)
data: the data to read, can be a primitive type (eg. float) or a custom struct
A reference to the data passed in
1#include <EEPROM.h>2
3struct MyObject{4 float field1;5 byte field2;6 char name[10];7};8
9void setup(){10
11 float f = 0.00f; //Variable to store data read from EEPROM.12 int eeAddress = 0; //EEPROM address to start reading from13
14 Serial.begin( 9600 );15 while (!Serial) {16 ; // wait for serial port to connect. Needed for Leonardo only17 }18 Serial.print( "Read float from EEPROM: " );19
20 //Get the float data from the EEPROM at position 'eeAddress'21 EEPROM.get( eeAddress, f );22 Serial.println( f, 3 ); //This may print 'ovf, nan' if the data inside the EEPROM is not a valid float.23
24 // get() can be used with custom structures too.25 eeAddress = sizeof(float); //Move address to the next byte after float 'f'.26 MyObject customVar; //Variable to store custom object read from EEPROM.27 EEPROM.get( eeAddress, customVar );28
29 Serial.println( "Read custom object from EEPROM: " );30 Serial.println( customVar.field1 );31 Serial.println( customVar.field2 );32 Serial.println( customVar.name );33}34
35void loop(){ /* Empty loop */ }put()Write any data type or object to the EEPROM.
1EEPROM.put(address, data)address: the location to write to, starting from 0 (int)
data: the data to write, can be a primitive type (eg. float) or a custom struct
A reference to the data passed in
Note: This function uses EEPROM.update() to perform the write, so does not rewrites the value if it didn't change.
1#include <EEPROM.h>2
3struct MyObject {4 float field1;5 byte field2;6 char name[10];7};8
9void setup() {10
11 Serial.begin(9600);12 while (!Serial) {13 ; // wait for serial port to connect. Needed for native USB port only14 }15
16 float f = 123.456f; //Variable to store in EEPROM.17 int eeAddress = 0; //Location we want the data to be put.18
19
20 //One simple call, with the address first and the object second.21 EEPROM.put(eeAddress, f);22
23 Serial.println("Written float data type!");24
25 /** Put is designed for use with custom structures also. **/26
27 //Data to store.28 MyObject customVar = {29 3.14f,30 65,31 "Working!"32 };33
34 eeAddress += sizeof(float); //Move address to the next byte after float 'f'.35
36 EEPROM.put(eeAddress, customVar);37 Serial.print("Written custom data type! \n\nView the example sketch eeprom_get to see how you can retrieve the values!");38}39
40void loop() { /* Empty loop */ }EEPROM[]This operator allows using the identifier
EEPROM1EEPROM[address]address: the location to read/write from, starting from 0 (int)
A reference to the EEPROM cell
1#include <EEPROM.h>2
3void setup(){4
5 unsigned char val;6
7 //Read first EEPROM cell.8 val = EEPROM[ 0 ];9
10 //Write first EEPROM cell.11 EEPROM[ 0 ] = val;12
13 //Compare contents14 if( val == EEPROM[ 0 ] ){15 //Do something...16 }17}18
19void loop(){ /* Empty loop */ }length()This function returns an unsigned int containing the number of cells in the EEPROM.
This function returns an
unsigned int1EEPROM.length()Number of cells in the EEPROM as an
unsigned int