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Grosvenor AX25 and AMTOR

Posted: Sun May 19, 2019 1:01 am
by dlinsley
Includes the ROM dump and some photos of both the inside and outside of the cartridge.

Re: Grosvenor AX25 and AMTOR

Posted: Sat Jul 13, 2019 6:17 pm
by Pernod70
Has anyone taken a look at this?

Considering it's a 32K ROM I'd assumed that the switch would simply select which half is paged in so that each program can be called with EXEC 49152. This doesn't seem to be the case so I'm wondering if they've switched some data lines to obfuscate the code. Need to take a closer look at the photos.

Re: Grosvenor AX25 and AMTOR

Posted: Sun Jul 14, 2019 3:01 am
by Pernod70
Success! The ROM is definitely encrypted.

The address lines A0 and A1 are swapped, and the switch selects which half of the ROM is addressed with line A14.

The data lines are also swapped in order MSB 3, 2, 1, 0, 7, 6, 5, 4 LSB.
0013.png
0013.png (1.85 KiB) Viewed 5214 times
0014.png
0014.png (1.37 KiB) Viewed 5214 times