Questions tagged [6845]

Questions about the Motorola MC6845 CRT Controller chip, or clones of it (e.g. MOS 6545).

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16 votes
4 answers
2k views

Is it possible to detect a CGA card on an IBM PC 5150 by write/reading the Motorola 6845?

I am trying to programatically detect the CGA card on old IBM 5150-ish PCs. The Paku Paku game source code doesn't directly detect it. The strategy is to detect VGA, EGA, Tandy, PCJr, etc etc, then if ...
8 votes
1 answer
741 views

How does the Motorola MC6845 in the Amstrad CPC 464 behave on start-up?

I'm trying to emulate an Amstrad CPC 464. I'm having trouble to understand how its Motorola MC6845 CRTC chip behaves on start-up. The boot ROM sets up the CRTC registers pretty early on, but if I ...
11 votes
2 answers
380 views

Which addresses does the Motorola 6845 CRTC output during retrace?

I'm trying to understand how the video hardware (CRTC and Gate Array) in Amstrad CPCs works. Specifically, I have a question about the behavior of the refresh memory addresses and row adresses output ...
16 votes
1 answer
1k views

How did the Commodore PET 80 column display work?

Some variants of the Commodore PET (e.g. the 8000 and 9000 series, as well as some other versions with an aftermarket add-on) produce an 80x25 character display. Their character set is fixed in ROM ...