Hello,
Have a look at AN2346, where a method of distributing wear over a whole flash block is detailed. Sample assembly code is also given.
I believe there are two restraints - the total number of program/erase cycles per byte within a block, and the total accumulated time that high voltage is applied to a row, between erases, should not exceed a certain limit. It is OK to program different bytes in the same row, at different times. The big no-no is that no one byte should be programmed more than once, without an intervening erase.
For the HC908QT/QY series (and I assume other HC908 of similar vintage) the row erase endurance is specified as minimum 10k cycles, and the row program endurance is specified as minimum 10k cycles - these are separate specifications. The cumulative program HV period is 4 milliseconds maximum.
These figures would indicate, assuming four updates per day, and without wear distribution, a very conservative flash lifetime of about 7 years.
Regards,
Mac
Message Edited by bigmac on 2006-11-2301:07 AM