EEPROM Read
The microcontroller on the Arduino and Genuino boards have 512 bytes of EEPROM: memory whose values are kept when the board is turned off (like a tiny hard drive).
This example illustrates how to read the value of each byte EEPROM using the EEPROM.read() function, and how to print those values to the serial window of the Arduino Software (IDE).
Hardware Required
- Arduino or Genuino Board
Circuit
There is no circuit for this example.
image developed using Fritzing. For more circuit examples, see the Fritzing project page
Schematics
image developed using Fritzing. For more circuit examples, see the Fritzing project page
Code
/*
* EEPROM Read
*
* Reads the value of each byte of the EEPROM and prints it
* to the computer.
* This example code is in the public domain.
*/
#include <EEPROM.h>
// start reading from the first byte (address 0) of the EEPROM
int address = 0;
byte value;
void setup() {
// initialize serial and wait for port to open:
Serial.begin(9600);
while (!Serial) {
; // wait for serial port to connect. Needed for native USB port only
}
}
void loop() {
// read a byte from the current address of the EEPROM
value = EEPROM.read(address);
Serial.print(address);
Serial.print("\t");
Serial.print(value, DEC);
Serial.println();
/***
Advance to the next address, when at the end restart at the beginning.
Larger AVR processors have larger EEPROM sizes, E.g:
- Arduno Duemilanove: 512b EEPROM storage.
- Arduino Uno: 1kb EEPROM storage.
- Arduino Mega: 4kb EEPROM storage.
Rather than hard-coding the length, you should use the pre-provided length function.
This will make your code portable to all AVR processors.
***/
address = address + 1;
if (address == EEPROM.length()) {
address = 0;
}
/***
As the EEPROM sizes are powers of two, wrapping (preventing overflow) of an
EEPROM address is also doable by a bitwise and of the length - 1.
++address &= EEPROM.length() - 1;
***/
delay(500);
}
* EEPROM Read
*
* Reads the value of each byte of the EEPROM and prints it
* to the computer.
* This example code is in the public domain.
*/
#include <EEPROM.h>
// start reading from the first byte (address 0) of the EEPROM
int address = 0;
byte value;
void setup() {
// initialize serial and wait for port to open:
Serial.begin(9600);
while (!Serial) {
; // wait for serial port to connect. Needed for native USB port only
}
}
void loop() {
// read a byte from the current address of the EEPROM
value = EEPROM.read(address);
Serial.print(address);
Serial.print("\t");
Serial.print(value, DEC);
Serial.println();
/***
Advance to the next address, when at the end restart at the beginning.
Larger AVR processors have larger EEPROM sizes, E.g:
- Arduno Duemilanove: 512b EEPROM storage.
- Arduino Uno: 1kb EEPROM storage.
- Arduino Mega: 4kb EEPROM storage.
Rather than hard-coding the length, you should use the pre-provided length function.
This will make your code portable to all AVR processors.
***/
address = address + 1;
if (address == EEPROM.length()) {
address = 0;
}
/***
As the EEPROM sizes are powers of two, wrapping (preventing overflow) of an
EEPROM address is also doable by a bitwise and of the length - 1.
++address &= EEPROM.length() - 1;
***/
delay(500);
}
See also
- EEPROM.read()
- serial.begin()
- serial.print()
- EEPROM library reference
- EEPROM Clear - Fills the content of the EEPROM memory with “0”.
- EEPROM Write – Stores values read from A0 into EEPROM.
- EEPROM Crc – Calculates the CRC of EEPROM contents as if it was an array.
- EEPROM Iteration – Programming examples on how to go through the EEPROM memory locations.
- EEPROM Put – Put values in EEPROM using variable semantics (differs from EEPROM.write() ).
- EEPROM Get – Get values from EEPROM and prints as float on serial.
- EEPROM Update – Stores values read from A0 into EEPROM, writing the value only if different, to increase EEPROM life.
Last revision 2018/05/17 by SM
