Re: PCbox, an add to the MS-DOS 1.25 project

Den Mon, 16 Oct 2017 13:37:46 +0000 (UTC) skrev Steve Gray
<sjgray@rogers.com>:
> Hi,
> In fact Mike and I have been discussing an 8088 (or higher) version
> of the SoftBox for a couple years now. I also have a Softbox
> (http://www.6502.org/users/sjgray/projects/softbox/index.html)  and
> helped Mike with the CBM-II port (fun fact, the port also runs on the
> P500 and might be the only P500 hardware add-on!). We also discussed
> a 6809 Softbox for OS/9 or NitrOS, and a version that could be used
> on a C64/C128 or other CBM using the parallel port or add-on IEEE
> interface. We also talked about  the possibility of creating a new
> PCB.  Mike is currently pre-occupied with NON-CBM stuff (sorry
> Mike ;-)  ) but with a little encouragement he might be persuaded to
> continue on the SoftBox. Steve

There is already a general 6809 card for 6502 machines - atleast
developed on/for Atari 8-bit computers but should work in any 6502
machine. Of course on a PET it would be better to make a copy of the
CBM 6809 card, but on other Commodore 8-bit machines it would be nice
with a card which switches between 6502/6510/8502/6509 and 6809.

But why not go all the way and add some 68k chip? :)

Regarding adding a CPU internal to the computer, the basic problem is
that 6502 and 6800 CPU's leave every other "half cycle" on the bus free
for other use, specifically video hardware in CBM computers, but
8080/8085/Z80/8088 doesn't work that way. That is also the reason for
the Z80 being so slow in C128 compared to other Z80 implementations.

Something that would be really really cool is an add-on to C128 making
it possible to switch between Z80 and an 8088 (or even replace the
Z80). Add some hardware that traps access to certain memory and I/O
areas and let the 8502 handle those traps. That way it could be more or
less completely IBM PC compatible. (Emulating CGA on the C128 80 column
hardware would be rather slow, but it could work. MS-DOS anyway support
"MODE CO40" for 40 column display. With the apropriate hardware
remapping adresses it could be possible to make the VIC-II screen and
color memory appear the same way as CGA in 40 column text mode).

But if you aim for a SoftBox but with 8088, I'd also suggest some
hardware to handle accesses to special memory and I/O adresses, but
that would have to be handled by the 8088 CPU (unless another CPU is
added to that board).

But how about an S-100 bus card that makes a Commodore 8-bit computer
a console for any S-100 bus computer? :)

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