Re: CBM-II Character Set and Colour Expansion (was: BASIC for the CBM-II/8088)

Den Wed, 11 Jul 2018 00:06:29 +0000 (UTC) skrev Steve Gray
<sjgray@rogers.com>:
> I've looked again at the schematics and yes, this is possible. My
> Colour-Bee block diagram is basically the attribute RAM. I'd put 2K
> at $C000-C7FF. We should be able to piggyback this 2K on the existing
> video ram socket with a small adapter. This means the ram will
> already be "behind" the cpu/crtc multiplexers (U14,U15,U22 of the HP
> schematics) again as in my block diagram. Perhaps we could put
> another 2K at $C800-CFFF for future software defined fonts (I am
> currently working on a PET soft-font system which should be adaptable
> to the CBM-II). The 256 character set expansion would be a simple ROM
> to EPROM adapter for U41 that doubles the size (2764 EPROM) and
> inserts DOTD7 between A10 and A11. Then the REVID line is disabled by
> grounding PIN5 of U63. I've noticed that for the most part the VIDEO
> RAM and CHR ROM are both socketed so this shouldn't be too much
> trouble. Steve

In some kind of distant long-run we should probably aim for a revised
motherboard where all different wanted/supported CPU's can access ram
at the same time, and make the video hardware a crossover between CBM
and PC video hardware (not that hard since they are all based on the
6845/6545).

Mixing 8088 and/or Z80 with 6502/6809 buses seems like the tricky part
though.

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