Re: A89: Writing to Flash ROM
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Re: A89: Writing to Flash ROM
I have checked now. an erased byte is $FF, so you can only add extra zeroes to
an un-erased byte (if you can change it at all)
the smallest block you can erase is one block, that is 64KB.
So, in order to patch a few bytes, you have to backup that block, erase it, and
write it back into place. quite risky.
I _really_ don't recommend to do this on the first block in the writable flash
(the second in total, the one right after the first :) (1 or 2, depending on how
you number them))
before you really know what you are doeing and have tried the routine on other
blocks. and at least tripple check that you change all data neded when you
change it to patch that second block.
The reason is that the bootloader checks some bytes in the beginning of this
area, (don't remember wich) and if they are wrong, your calc will refuse to
boot, even before giving you the chance to upload a new rom, and thus render
your calc totally useless. There is no way of fixing it then, without
desoldering the flash and hook it up in an external flashprogrammer.
//Olle
Olle Hedman wrote:
> Another thing about the write then. I'm quite shure you can only write ones (or
> zeros) without eraseing the area first. (most flash:es work like that.)
> I have to look through the pdf for the flash to be shure though.
> maybe that is your problem?
> I assume you have the pdf for the flash. If not, you can download it from me at
> http://alh.dhs.org/ti89/
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