Re: Things to do with an extra 65C816 CPU

["Henry Broekhuyse" <broekh@unixg.ubc.ca>]

Bryan Villados <news001@nospam_macgeek.org> wrote in message
news:090920002304524767%news001@nospam_macgeek.org...
> Could you guys please recommend any project ideas I could play around
> with that would utilize this chip? I've been looking around for
> projects made in the early to mid 70's that utilized chips like the
> 8008, 8080, 6502 and the Z-80. What I'm particularly interested in is
> building something that I could show in my museum demonstrating to
> people the entry of machine language code, much like they did with the
> MITS Altair 8800 and the Mark-8. Y'know, flipping switches and pressing
> the "enter" button. You can actually see a Mark-8 on sale right now at:
>
> <http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=429053120>
>
> Showing machine language entry via the monitor on the Apple II isn't
> impressive enough for demonstration purposes. If I can make a simple
> 65C816 based unit that processes simple arithmetic operations and blink
> LEDs much like the machines I mentioned would be really cool to make.

The kind of hardware project you are contemplating is feasible, if you have
a lot of time to work on it. Using "modern" components (like "byte-wide"
memory chips) it is possible to reduce the component count and amount of
work required (compared to building, say,  the Mark-8 you referred to
above). However, this is still a complex project if you are doing it "from
scratch".

The 65C816 is probably not a good choice for building the kind of
demonstration system you want, because of its more complex 8/16 bit design.
For the kind of system you are contemplating, a "simpler" processor would be
easier to design around and would be more than adequate for running the kind
of demonstration you are interested in.  Both the 6502 and Z80 can still be
bought new from parts distributors and cost only a few dollars.

The "vintage" computers you referred to (like the Mark-8, Altair, and IMSAI)
with the "blinking lights" that impress people did not have a monitor
program in ROM. The front panels on these machines were very simple designs
* that used a few hardware tricks to run/stop/single-step the processor and
to read/write individual memory locations. With a new design it would be
easier to "simulate" these functions in software by writing a "monitor"
program stored in ROM which would control the front panel lights and
switches.

* "simple design" =  implemented with standard logic chips, but a lot of
them!

Keep in mind that the novelty of entering even a few bytes (let alone
programming) with one of these front panels wears off very quickly. Even
entering a program to do "simple" arithmetic (even adding two 8-bit binary
numbers) can get tedious when done via a front panel, and the result (other
than the blinking lights) is less than impressive unless the user can think
well in binary.