Grosvenor AX25 and AMTOR

Use this forum to submit new files for the download section of the archive. I will check each submission and upload it to the archive on a regular basis.
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dlinsley
Posts: 44
Joined: Thu Dec 10, 2009 8:15 pm
Location: Seattle, USA (formerly Chester-le-Street, UK)

Grosvenor AX25 and AMTOR

Post by dlinsley » Sun May 19, 2019 1:01 am

Includes the ROM dump and some photos of both the inside and outside of the cartridge.
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Grosvenor AX25 and AMTOR.zip
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Pernod70
Posts: 75
Joined: Sat Apr 22, 2017 10:06 pm
Location: Croydon, UK

Re: Grosvenor AX25 and AMTOR

Post by Pernod70 » Sat Jul 13, 2019 6:17 pm

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.

Pernod70
Posts: 75
Joined: Sat Apr 22, 2017 10:06 pm
Location: Croydon, UK

Re: Grosvenor AX25 and AMTOR

Post by Pernod70 » Sun Jul 14, 2019 3:01 am

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 222 times
0014.png
0014.png (1.37 KiB) Viewed 222 times

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