18F2550 Program Memory

[arunkish]

Hello All

I am using 18F2550, and I am trying to write to the ROM using write_program_eeprom() function, but it is not working. Will this PIC support this function or should I turn on/off some fuses? I have learned that in some PIC's a total of 32 or 64 bytes has to be written at a time. How can I do that? Please advise.

Thanks

[Ttelmah]

First thing, give your compiler version?.

The current versions do write correctly to this chip, but there is no guarantee that your version does, if it is old.

Then you need to understand, that a 'write', can only change bits from the erased state, to the other state. You can't set a bit to '1' with a write.

Now on this chip, erases can only be done 64bytes at a time. Writes can be done 32bytes at a time.

The write_program_memory function, will automatically perform an erase, if you write to the first byte of a page. The write_program_eeprom function, does not perform an erase. Most of the later chips do support single byte writes (which is why this function exists), but this one doesn't.

The sequence you need, is to read the whole of a 64byte block to the page boundary below the byte you want to change.
Then change the single byte you want in this table in RAM.
Then write the whole 64byte byte block back, with write_program_memory (which will automatically trigger an erase).

[arunkish]

Sorry for the delayed reply. Thank you so much for your TIP. I am using a very old version of compiler 3.222.

Thanks a lot.