will EEPROM keep values after reprogramming?

Forum 2005-2010 (read only) General Frequently-Asked Questions
1

Hi,

If I write values to the atmega's EEPROM, can I read them after I have reprogrammed the chip with another program more designed for reading and printing the eeprom values?

Joachim

2

According to the design indicated in the ATmega382 datasheet the EEPROM should be stored and accessed in a completely different location from the flash programmable memory.

But if its critical data, do a test first.

3

Data sheet link: http://www.atmel.com/dyn/resources/prod_documents/doc8161.pdf

4

thnx, not very critical...

Joachim

5

It is a physically separate memory. I've never tried, but I think I read somewhere you can program the EEPROM through the programmer but if you don't, it should stay unchanged.

In any event, as far as I know, the Arduino bootloader should not alter the EEPROM.

6 
If I write values to the atmega's EEPROM, can I read them after I have reprogrammed the chip..

Yes, it will be retained also after you upload a new sketch when using the standard Arduino IDE configuration.

The Arduino bootloader (in its most recent incarnation) can alter/program EEPROM, but will only do so if you manually start the uploader (avrdude) and instruct it to do so.

If you upload a new sketch through an external programmer (e.g. AVR ISP, STK500 etc.), the default behavior however is to erase the chip (flash and eeprom) prior to programming. There is however a fuse setting available (on the ATmega's) that can be enabled so that EEPROM is preserved through the erase cycle.