AVR Freaks

Hello Marco,

The AVR EEPROM is guaranteed to withstand 100K write/erase cycles. If you estimate you'll power down your chip more times than this, you should take advantage of the entire EEPROM by using a cyclic algorithm or something to the effect. If your requirements still haven't been met, you should begin to consider external components.

Best regards,

Morten, AVR tech. support, Atmel FAE

Marco,

you Wrote ;-

>eeprom int a = 0;
>value of 'a' will be stored into internal eeprom, now if I set a = 5; immediatly eeprom will be update
>with the new value, is it right ?. So I have to check how many times I change eeprom stored data
>values instead how many times I "power down" chip, isn't it ?

That is right..
What I have on my synthesiser are a couple of menus, when you EXIT a menu it saves ALL the parameters to EEPROM, but ONLY when you exit a menu, I made a function called eeprom_write();
which writes to the eeprom when its called.
This way I can change the values in the program but only write to them once..

I'll explain how I do this ;-

int a = 0; // working value of a variable
eeprom int a_eeprom ; // value stored in eeprom

You'll notice I havent given 'a_eeprom' any value..
Now you have two variables, use 'a' whilst your normal program runs,

During startup, to recall a value from eeprom you can now do this;-

a = a_eeprom ; // get value from eeprom

Then when you need to save it simply do ;-

a_eeprom = a ; // save value to eeprom

this reduces the number of writes to the eeprom,
But does mean you need to have a "save settings" option in your software (maybe a button?)

Hope this helps
Paul Maddox

Http://www.wavesynth.com/

Marco,

The other thign you could do , if its a radio, ia combination of Grants idea and an additional idea.

Read the value from your tuneing dial (assuming this is what you want to store) then if the value is different to eeprom value AND the new value hasnt schanged to 10 seconds then write to the eerpom.
In this way you write when a value has changed but only if its not constatly changing (ie, tuneing in a new station).. I would imagine you may be able to increase the 10 seconds, as after tuning in a station you would listen to it for longer than 10 seconds before turning off the receiver.
so anything up to a few minuets would be ok..

The points Peter makes about resetting address register and 10seconds after reset are VERY good points and worth remembering..

Paul Maddox

Http://www.wavesynth.com/

Marco,

The reason for resetting the register (as Ive been led to beleive) is that sometimes on power down the EEPROM can mistakenly have data written to it.. if you reset the register to ZERO and avoid putting any data in the first byte you will avoid this 'slight' bug... I have to say Ive NEVER had this happen to me (on the projects where Ive forgotten to reset the register) but I have heard of people who have, its just a pre-caution..

Paul

Http://www.wavesynth.com/