write_program_eeprom question

[jventerprises]

the manual says:

WRITE_PROGRAM_EEPROM - Writes 2 bytes, no erase is needed

Does this mean that the CCS code reads a block, modifies the 2 bytes, and then writes the entire block back?

Or, does is just write the two bytes and I am responsible for having pre-erased the appropriate locations?
_________________
Jon

[bkamen]

You have to follow the rules outlined in the datasheet for erasing blocks.

There is usually a minimum page erase size.

So while you can write the bytes back 2 at a time, you may wipe out 1024 bytes while prepping to write those 2.

That's what you need to keep in mind.

If you're using the Prog FLASH as EEPROM, then you also need to make sure the PIC has enough room to hold 1 page so you can read it all, modify what you want and then write it back, 2 bytes at a time or more.

-Ben
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Dazed and confused? I don't think so. Just "plain lost" will do. :D

[PCM programmer]

You didn't give your PIC, so I looked at the .LST file for an 18F452.
The write_program_eeprom() doesn't do an erase. It does a read-
modify-write operation on 2 bytes in a 8-byte block in program flash
memory. There is no erase.

But if you look at the .LST file code for write_program_memory(),
you will see the Erase code. It's similar to the ASM example shown
in the 18F452 data sheet. In other words, in a case where an erase
is needed, the compiler puts in the code to do it. You don't have to
worry about it.

[dgoldman]

For the 452 with write_program_eeprom(), the erase is handled automatically? Great!

The data sheet shows erase is only automatic when writing FLASH_WRITE_SIZE (64) bytes. This requires write_program_memory() I assume. Compiler to the rescue I guess.

Write_program_eeprom() can write 2 bytes anywhere in program memory without erasing? If I need to write more than 2 bytes, I should use write_program_memory() and stick with FLASH_WRITE_SIZE length to assure efficiency?


So is it generally good practice to then read and checksum to verify the write?

[bkamen]