Dear PICCERs,

I have a task, where I have to build a operation time counter, means
somethings, which adds the time a device was switched on. There is only a 5V
DC supply, if 5V is present the device works, if not, the device is switched
off.
The total time to be checked is 5 years and the resolution has to be 1
minute.
Now first the task is very simple: When the PIC (I intend to use a 12F629)
is powered up, it reads the already elapsed time from EEPROM, then simply
starts to count minutes (by TMR1 and an added software divider) and when a
minute is over it stores the new total time into EEPROM. 
Now the problem is, when calculating the total number of storages you'll get
5 years x 365 days x 24 hours x 60 minutes = about 2,6 x 10E6 write cycles,
but the spec only says 10E6 cycles for EEPROM memory.
Further thinking showed that the result is never bigger than 3 Bytes
(FFFFF&h = 16,7 x 10E6) and the high and middle byte can be stored only, if
they have changed, so I have no more than 2,6x10E6 / 256 = about 10000 write
cycles for the middle byte and even 2,6x10E6 / 65536 = 40 write cycles for
the high byte which is inside spec.
The problem is to find a way to store 2,6x10E6 time one byte into EEPROM. 

Has anybody an idea? Any help greatly appreciated!


Best regards

Peter



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