what ROM do I have?

[1024MAK]

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

Just for the record, a "550" ROM should produce:

Code: Select all

3901          253
3902          203
3903          53
3904          254
3905          24
3906          5
3907          62

See also this topic

Mark

[bola_dor]

Thanks a lot!!

[MarcNL]

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

[Moggy]

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!

[XavSnap]

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.

[1024MAK]

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

Yes, true.

Mark

[stroebeljc]

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.