Sinclair ZX80 / ZX81 / Z88 Forums

Um, I think the checksums for the 622 and the 649 in Moggy’s post may be swapped

I was just checking a Zeddy ROM, and it’s definitely a “649” type, the checksum from the BASIC program listed earlier in this topic is 855106.

If you use: It should print the following for a “649” type And for a “622” type it should print the following Just for the record, a "550" ROM should produce: See also this topic

Mark

Thanks a lot!!

If only the order of bytes for the pause command are swapped, then this (simple) checksum would be the same.

1024MAK wrote: ↑Sun Jan 30, 2022 12:16 am Um, I think the checksums for the 622 and the 649 in Moggy’s post may be swapped

I was just checking a Zeddy ROM, and it’s definitely a “649” type, the checksum from the BASIC program listed earlier in this topic is 855106.

If you use:

Code: Select all

10 FOR A=3901 TO 3907
20 PRINT A,PEEK A
30 NEXT A

It should print the following for a “649” type

Code: Select all

3901          253
3902          54
3903          53
3904          255
3905          205
3906          7
3907          2

And for a “622” type it should print the following

Code: Select all

3901          205
3902          7
3903          2
3904          253
3905          54
3906          53
3907          255

See also this topic

Mark

I've lost the will to live and no longer give a toss!

Hi,

If you had to launch a checksum test, you had to unplug all external device...

The Memotech I/F, the Memotext, Memocalc, the Memotech HRG or a &1F00 IR UDG RAM... drive any memory offsets to another locations.
The checksum may be wrong.

MarcNL wrote: ↑Sun Jan 30, 2022 1:35 am If only the order of bytes for the pause command are swapped, then this (simple) checksum would be the same.

Yes, true.

Mark

Since checksums are so 1980s and don't actually work to resolve whether you have ZX81 ROM Edition 2 or 3, here is a 1k program that calculates the ROM's CRC16-CCITT to identify its version.
The source is on github.