Re: homebrew computer - where to start?

May even run across some links to the Altair 8080 systems that preceeded
many "user Friendly" devices. These were once offeres in a kit of parts and
fair instruction manual. Basic, if my memory serves me, was the op-sys du
jour. Others may corect me if in error?? Item I had actually used Octal
Nixie Tubes for Hex Dec output which we manually decoded.
"Michael Black" <et472@xxxxxxxxxxxxxxxxxxx> wrote in message
news:dfd7rt$k6o$1@xxxxxxxxxxxxxxxxx
>
> Charles Jean (alchemcj@xxxxxxxxxxxxx) writes:
>
>> If you can stand starting at the microprocessor level, try getting
>> your hands on "Build Your Own Z80 Computer" by Steve Ciarcia, BYTE
>> Books, McGraw-Hill, circa 1981, ISBN 0-07-010962-1.
>>
>> Sounds like it might be just what your 'e looking for.
>> Cheers!
>> Charlie
>
> I've never looked closely at the book, but my impression was that it
> was to build a working system, circa whatever year it came out.
>
> No matter how fancy a system was back then, it's going to be nothing
> compared to what you can find in the garbage today. Thus I think
> there's little reason to build a computer to that extent.
>
> I think there's still plenty of reason to have something on the level
> of the KIM-1, ie a calculator style keyboard and readout, a good monitor
> that can single step etc, a cassette interface to save programs, and
> some sort of general purpose I/O so you can play with things. There
> were plenty of such single board computers back then, I use the KIM-1
> as an example because I had one as my first computer.
>
> But the single stepping meant you could run programs and see what
> happened at every step. You could even just put in a line of code,
> and check that out, really useful to getting a real feel for
> what the op-codes were supposed to do. Since there was so little
> in there, you didn't need to learn a whole lot of GUI stuff before
> you tried out your simple program to add some numbers. The monitor
> did have what you needed.
>
> The general I/O meant that you could play with real things, like
> hook some LEDs onto it and learn how to control them. Or have
> inputs from something, to control the program.
>
> These computers are of such a simple level that they are easy to build,
> and you will get ample use of it (as opposed to trying to build a full
> blown S-100 bus computer from 1976, which would have real limitations
> today if you wanted to run applications). In some ways, it's even easier,
> because whereas the KIM-1 needed 8 ICs to get 1K of memory, you can
> scrounge up a static RAM that fills the address space that will draw
> less current and require much less wiring. If you can live with
> hooking it up to a terminal (ie your home computer running a terminal
> emulator), then you can toss the readout and keyboard. Many of
> those old boards allowed for hooking up a terminal to an RS-232 port,
> though many of us didn't since the terminal cost more than the computer.
> Likewise, one could use the home computer to store the programs, which
> beats out a cassette interface in terms of speed and reliability.
>
> ONe great project from the era was in Byte, though I can't remember the
> year, or even a general idea. 1978 and 1980 somehow come to mind.
> Someone
> wrote an article about bootstrapping an 8085. Jam a NOP onto the data
> bus, so the processor advances the address bus while doing nothing. By
> single stepping, this means you can load the RAM without any bootstrap
> ROM. The input mechanism was a piece of circuit board that he'd carved
> up with a hacksaw to make pads, and a "stylus" to connect a wire to
> the needed pad. Some LEDs on the data bus. Not much else. Build
> up the simple hardware, he just used wire to do it if I recall, and
> you can start playing right away. None of that fussing with a bootstrap
> ROM, but something you can infinitely play with it. Get some coding in,
> and then add that monitor ROM. Or dig up the listing from an old single
> board computer, and use that.
>
> SOme years later, Byte put out a book about the 68000, and it had
> an article (which I think had never run in Byte because I never
> saw it elsewhere) using similar techniques to bootstrap the 68000.
>
> Michael
>


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