C64-C128 CP-M Cartridge Interest
lynchaj at yahoo.com
Sat Dec 25 08:38:34 CST 2010
C64/C128 CP/M Cartridge Interest?
Jim Brain brain at jbrain.com
Fri Dec 24 22:37:23 CST 2010
> N8VEM is a good candidate...
A couple of reasons:
* N8VEM, while a great solution, is enormous. There are many closet
C128 CP/M users, and they'd never go for such a huge addition to
their setup. A cartridge form factor, easy decision. Others
would scoff at relegating their C128 as a dumb terminal to another
machine (for instance, they could easily do the same thing by
running a CP/M emu on their PC and connecting the C128 to the PC
via a null modem cable). It's perception.
* There is more to a C128 CP/M cartridge than just using the C128 as
a dumb terminal. Some C128 CP/M apps might take advantage of the
functions in the C128 itself, like the 40 column screen and such.
Thus, memory mirroring and such would be useful. I didn't bring
it up initially, because A) not sure if apps did that. B) I just
wanted to start small, and thought that interfacing the Z80 to the
CBM bus would be a good start
* I theorized that a tiny CP/M board might be of use where N8VEM was
too big or too expansive.
* I so want to start learning Verilog. I thought, if I got a
basic environment going, I could then take a look at virtualizing
the pieces to an FPGA connected to the C128/C64. But, since I
know little of Z80 and CP/M (having used it long ago), I thought
going to FPGAs from nothing was too large a leap.
* The next step after that is an accelerated CP/M. This plays in
with my hope to obtain the rights to the SuperCPU for the
C64/C128. It lacked accelerated Z80/CP/M compatibility, which I
thought I could add, though maybe not.
I'm gathering from the results that there might not be the interest I
had theorized, which is fine. But, I thought I'd at least ask.
I gather the form factor you have in mind is the classic C64 game cartridge?
The CP/M cartridge I recall from the 1980's was much larger than a game
cartridge so that's were I was coming from. I've never heard a Eurocard
board (160x100mm) described as "enormous" but clearly you are thinking about
a much smaller board than I was.
I suppose such a cartridge is possible but it would require a few very dense
parts. Probably a CPLD at a minimum probably a FGPA with fine pitch SMT
connections. At least to me, you would need a four chip minimum a Z80,
SRAM, Flash ROM, and glue logic. Maybe less if you can blow a Z80 core into
an FPGA which is possible I believe. All in SMT QFP packaging to get the
density to fit multiple chips into a 2"x3" PCB. It sounds more like a
commercial product than a hobbyist project to me though.
Actually, the C64 ECB bridge approach idea is not using the C64/C128 as only
dumb terminal. It would be 3 or so general purpose IO ports. Then the
C64/C128 could serve IO to the Z80 when it is running. The Z80 sends an IO
request to the C64 which passes status and data back. The 6510 would run an
IO server program and the Z80 would be its client. Assuming an interrupt
driven design the IO processor (6510) could serve the Z80 IO as a
"background" task to a limited extent.
This is how the N8VEM SBC with the 6809/6802/6502 host processor works. The
6809 runs independently but passes its IO requests to the Z80 which serves
terminal IO, disk IO, parallel port, video or whatever. It fully utilitizes
the Z80 and 6809 as a dual independent processors with their own RAM/ROM.
However the 6809 host processor can be optionally upgraded to include its
own unique IO set for more independence or as stand alone mode.
I am not familiar with the SuperCPU but based on quick web search it appears
to be roughly Eurocard sized. Good luck with your project.
Thanks and have a nice day!
PS, we had a builder recently who crafted his own N8VEM SBC using a CPLD
design. Basically it was all the large IC s (CPU, RAM, ROM, UART, PPI) and
one large CPLD. It seemed to work well enough too. I was considering doing
something similar on the N8VEM home computer project since it is limited to
60 square inches. However, we seemed to have resolved the PCB layout issues
using regular PTH DIP/PLCC 2 layer PCB construction.
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