IMSAI News?

From: Richard Erlacher <edick_at_idcomm.com>
Date: Sat Jun 15 15:40:58 2002

see below, plz.

Dick

----- Original Message -----
From: "Tony Duell" <ard_at_p850ug1.demon.co.uk>
To: <cctalk_at_classiccmp.org>
Sent: Saturday, June 15, 2002 12:30 PM
Subject: Re: IMSAI News?


> >
> > Last I spoke with the people at Imsai, the machine had some major issues
> > in my eyes...
> >
> > First, its no longer a S-100 box. (deal breaker right there)... None
> > of your existing
> > S-100 stuff can be used with the machine, and with no expansion bus,
> > Imsai has turned
> > one of the first open architecture boxes into something more like a Mac
> > (super-Eeeek!).
> >
> > Secondly, it was going to use a ISA VGA board for video display (Eeeek,
> > not ISA)!
>
>
> I am trying to figure out how this machine is in _any_ way superior to
> any of the following :
>
> 1) A CP/M machine with built-in video output (Epson QX10, etc). Not that
> much CP/M software used anything other than a text terminal.
>
> 2) A random collection of S100 cards from my junk box.
>
> 3) A Z80 single-board development system connected to my PC's serial port.
>
> All of the above would seem to do what the Imsai 2 would do -- and be
> easier to maintain, easier to expand, and plain more fun to use.
>
>
Sadly, I don't think you'll find anyone on this list who believes it is. I'm
not sure "superior" is an issue, however. If it were just, in some way,
compatible with what it seems it pretends to be.
>
> >
> > This last bit was really problematic becuse the Z800 cannot execute the
> > VGA bios code
> > in the ISA board's rom.
>
> Can't you get a VGA card where the registers are documented well enough
> to at least put the think into a simple text/graphics mode without using
> the BIOS ROM code? In other words, ignore the ROM and hit the hardware
> directly from the Z80? I know I'd have tried soemthing like that if I'd
> _had_ to use a VGA card with a CP/M machine...
>
The obvious solution, here, is to get a mono card. CP/M software didn't
support graphics unless the graphics were associated with a specific display
adapter anyway, so the use of a mono card, particularly one of the "short"
mono cards with two serial ports and parallel port on it would probably be
just the thing. Mono monitors are getting a mite scarce, however, but I still
have one or two, as I suspect many others do. The mono card is well
documented and does text at least as well as the best of terminals from back
in the '70's.
> >
> > These issues were enough for me to realize that the Series-2 machines
> > were not for me.
>
I doubt you're alone there, Tony.
>
> > But the idea of having a PC motherboard in there along with the Z800
> > ~could~ make for
> > a very interesting teaching platform. But once you have the PC
> > motherboard in there, why
> > run the actual Z800 CPU at all? Emulation would probably be much faster.
>
> If the Z80/Z800 bus was available to the user, then the reason for
> running the real hardware is obvious. But apparently it isn't.... This
> seems ridiculous...
>
That's why I didn't make time to become involved with the Imsai-II
development. I personally would have gone hog wild if he'd simply taken up
the Z80C0020 and run it at full speed on a CPU card complete with peripherals
(NOT Z80 peripherals!!!) that could easily be run without requiring that the
CPU never run faster than the slowest of them. An SCN 2681 and a simple MSI
parallel port would have worked fine, but an LSI like the 37C6-whatever-series
would have worked fine with it as well. That would have handled the need for
an FDC, 2 serial ports, a parallel port, and some other stuff one didn't have
to use. In fact, that combo with some sort of on-board MMU hardware would
quickly have made a whole and fully useable computer on a single S-100 board.
Off-board I/O would simply have required one slow the CPU down whenever an
off-board address was detected, which is simple enough. Using a PC keyboard
and a PC mono card (normally has no ROM code required for it, aside from
what's in the PC's system BIOS ROM, for which listings are readily available
and easily translated) would have handled the console interface readily enough
and making up a BIOS (remember, the BIOS normally is software under CP/M, not
firmware) that supports these as well as an IDE HDD would have been VERY
straightforward.
>
Received on Sat Jun 15 2002 - 15:40:58 BST

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