This discussion comes up from time-to-time. I recall giving the question
some thought. There is available on the 80C85 the HLDA pin, which was included
for implementing DMA. That input is not brought to the external bus connector,
but could be tied to an existing connector pin. That facility might make it
possible to do some interesting stuff..., I think.
I fear that this is a case of 'Just because it might be done, that doesn't
mean that it should be done'. Devoted hardware hackers are inclined to ignore
such caveats, however (Damn the practicality!..., this is man vs. machine!),
and I do not doubt that given sufficient resources of tenacity, someone could
churn out an interesting external (or internal) speed-up option.
John W.
----- Original Message -----
From: Ken Pettit
To: Model 100 Discussion
Sent: Tuesday, June 02, 2015 12:33 PM
Subject: Re: [M100] Upgrade via System Bus ?
I've actually looked at this before thinking it would be cool to have an
expansion bus plug-in device that is basically a new processor on the system
bus. Can't be done. The problem is that all the signals connecting to the
system bus are buffered, meaning they are one-way traffic only. The address
bus can only be driven by the 80C85 CPU and the data bus direction control is
the same.
Ken
On Tue, Jun 2, 2015 at 9:27 AM, Hiraghm <[email protected]> wrote:
Okay, so the system bus is used to connect to the DVI drive/video
expansion, but what are its total capabilities?
In an earlier message I wished for a cpu/ram upgrade for the M100. On
reading about the extRAM in Portable 100 issue November 1990 (page 17), I began
to wonder if one of you hardware types could build a very small cpu/ram upgrade
board that "takes over" for the CPU over the system bus.
Maybe this is how QUAD adds the banks of RAM, I don't know. That's why I'm
asking, because I don't know.
Not only would such a hardware upgrade speed up and expand the capability
of the M100 (would probably require a customized ROM via REX), but it would
make CP/M or even a custom FreeDOS (except FreeDOS is 32 bit :( ) possible.
