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phooky / VT100-Hax

DEC VT100 terminal ROM hacks for Retrocomp2014.
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mystery rom? #5

Open LegalizeAdulthood opened 7 years ago

LegalizeAdulthood commented 7 years ago

Is this the character generator ROM?

Was this a ROM placed in the sockets on the AVO board?

rdebath commented 7 years ago

There is a character ROM on the mainboard, but the mystery ROM does not contain character definitions or random data. It appears to contain 8080 machine code.

There is a slot for a character ROM on the AVO board, but a standard AVO board contains ONLY RAM. The CHAR ROM on the AVO board is intended for an extra 128 characters for extended character sets. Adding this ROM does not make the VT100 an 8-bit terminal (it's still 7-bit) but does enable ECS(0 and ESC(1 character selectors.

LegalizeAdulthood commented 7 years ago

OK, so that still leaves the question unanswered as to where this mystery ROM came from?

Was it in the ROM sockets on the AVO?

rdebath commented 7 years ago

Okay, I've just run a couple of quick tests.

The disassembly of the code is very similar to the first of the "normal" 2k ROMS.

If I use it as a replacement for "23-061E2.bin" I get a working VT100 emulator. So if I had to guess I'd say it might be copy of the ROM numbered "23-031E2.bin". But it could just as easily be a modified or later version.

Being this sort of ROM I don't think it'll work on the AVO.

LegalizeAdulthood commented 7 years ago

Interesting! That implies it is an earlier or later version of ROM 23-061E2.bin. I did a compare on it and you are correct that there are a few bytes that are different.