AVR microcontrollers are loaded with some amount of EEPROM (Electronically Erasable Read-Only memory ) memory. This is handy feature allowing developers to store program parameters like service information, constants, menu strings etc. Atmel states that AVR EEPROM memory can be rewritten over 1000000 times. Reading is unlimited.

In this article I am going to show how to store data to EEPROM by defining a variables.

For this we need to include eeprom.h header from avr directory (#include “avr/eeprom.h” ).

Then we can just write simple variable declaration using simple attribute EEMEM:

#include “inttypes.h”

#include “avr/io.h”

#include “avr/iom8.h”

#include “avr/eeprom.h”

//store initial byte to eeprom

uint8_t EEMEM eeprombyte=0×10;

//store initial word to eeprom

uint16_t EEMEM eepromword=0×5555;

//store string to eeprom

uint8_t EEMEM eepromstring[5]={”Test\0″};

int main(void)

{

//RAM byte variable

uint8_t RAMbyte;

//RAM word variable

uint16_t RAMword;

//RAM array of bytes

uint8_t RAMstring[5];

//read byte from EEPROm and store to RAM

RAMbyte = eeprom_read_byte(&eeprombyte);

//read word from EEPROM and store to RAM

RAMword = eeprom_read_word(&eepromword);

//copy string fro mEEPROM to RAM

eeprom_read_block ((void *)&RAMstring, (const void *)&eepromstring,5);

return (0);

}

EEMEM keyword indicates to compiler that variables are stored in EEPROM and it creates separate .eep file which has to be written to chip separately.

Se what I have got after compiling the above code:

Size after:

main.elf :

section size addr

.text 156 0

.data 0 8388704

.bss 0 8388704

.noinit 0 8388704

.eeprom 8 8454144

.stab 876 0

.stabstr 132 0

.debug_aranges 20 0

.debug_pubnames 74 0

.debug_info 486 0

.debug_abbrev 316 0

.debug_line 240 0

.debug_str 271 0

Total 2579

You can see compiler information about compiled code sizes. The bold line is indicating the size of occupied EEPROM memory. In this particular case we see that size is 8 bytes: one byte variable, one word (two bytes) and five byte array – total 8bytes.

Open .eep file located in project folder. The compiler compiled Intel Hex File of EEPROM data:

:0800000054657374005555109E

:00000001FF

The first line shows 8 byte data stored at address location 0. Second line is the same for all hex files – it indicates end of file record.

Dont forget, that .eep file has to be written to avr microcontroller separately as writing compiled program doesn’t write EEPROM data. If you use PonyProg programmer and AVR ISP cable this can be done easily. Open .eep file by selecting File->Open Data (EEPROM) File…and then select command: Command->Write Data (EEPROM). The same can be done with tool-bar buttons.

In the memory viewer there are both memory locations displayed: Flash and EEPROM. You may noticed that EEPROM memory area has different color than Flash. I hope you get the picture and can start working with AVR EEPROM memory.

You can download the source files of the AVR EEPROM using WinAVR example to try by yourself.

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This entry was posted on Saturday, July 1st, 2006 at 2:03 pm and is filed under AVR Microcontrollers. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.