I'm trying to write a prog to parse .89* programs on the PC. Verifying the checksum on variable files is working as expected. Verifying the checksum on flash files (.89k, .89u) is not working as expected.

Anybody got any experience with this that would be willing to help me understand what I am doing wrong?

Well, from documentation on the TI-89 file format: However, simplifying for a single variable, it says: There's a different format for Flash files, but the checksum is still the lower 16 bits of the sum of the variable data. Is there anywhere else where your bug could be coming from?

Thank you for the reply. The docs I have are

' TI-73...V200 Link Protocol Guide v1.4 by Tim Singer and Romain Liévin.'

As far as I can determine, these are the most recent docs in circulation. If there is anything more recent I would love to know.

Here's where I am having difficulty. The docs say that the checksum is calculated as a sum of all the bytes in the data section. Then take the lower 16 bits of that result and it should match up with the 2 bytes (in little endian format) at the end of the variable.

Working this for variable files (89p, 89y, 89z, etc. it works fine - no problem). But working it for a flash file (89k or 89u) does not calculate correctly for me.

I have made certain of the following:

The "data section" of a flash file starts at offset 0x4E - this is where I am starting
The last two bytes of the flash file should not be included in the checksum calculation.

So when I do this for a flash file, it does not add up. When I do it for a variable file - even one with multiple variables (89g) it works fine. I am trying to figure out what I am doing wrong here.