Back when Todd Fischer was starting the development of his Imsai-II I had
reservations about his plan to use a Z80 scion rather than the "real-McCoy,
and using an SMPSU that provided regulated supply rather than the traditional
unregulated supplies. Whe he asked me to become involved in the development I
had a full plate and couldn't do it, but I certainly didn't like the "smell"
of the notion of trying to compete in the rabidly competitive PC market, which
clearly what it looked like he was wanting to do.
Hoping to capitalize on the availability of low-cost PSU hardware, that having
been a major problem with the early S-100 hardware, and that being a major
weight/shipping-cost contributor, I think he was seeing the Z800, or whatever
it was, as a PC-competitive vehicle, which it wasn't. In fact, I don't
believe Zilog has anything capable of competing in that market at all.
If one wants a product that is both CP/M-80 capable and also able to run the
on-card firmware of ISA card peripherals, the V-40/V50 from NEC, and some of
their scions, though the later scions no longer have the 8080 core, which is a
problem, offer an alternative. The V40/V50 contain the serial I/O, timers,
DMAC's, interrupt hardware, etc, that readily support executing 8086-code,
thereby making the use of ISA boards straightforward, at least as part of the
CP/M BIOS. They also offer speed advanatages that can't be overlooked, but
generating the S-100 timing from their signals is not trivial and requires the
sacrifice of some performance. If one wants to "have is cake (in the form of
the 8080-compatible hardware execution unit) and eat it too (in the form of
the 8086 instruction set compatibility)," the V50 certain would be my choice.
I've built up a board that appears to generate the required timing from a V50
to run a basic S-100 interface compatible with late-70's (pre-IEEE 696
standard) S-100 hardware. Since I don't have an Imsai or Altair front-panel,
I have no way of ensuring that such a device would work with this board, and
since I've not had the time or motivation to get it done, I've not worked out
the details of swtiching back and forth between the 8080 execution unit and
the 8086 execution unit, which would be required to make all this stuff work
properly. One of these days ...
Dick
----- Original Message -----
From: "Bob Shannon" <bshannon_at_tiac.net>
To: <cctalk_at_classiccmp.org>
Sent: Saturday, June 15, 2002 8:04 AM
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)!
>
> This last bit was really problematic becuse the Z800 cannot execute the
> VGA bios code
> in the ISA board's rom.
>
> These issues were enough for me to realize that the Series-2 machines
> were not for me.
>
> 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.
>
> Loboyko Steve wrote:
>
> >Today, I noticed a link on Slashdot about the IMSAI
> >Series Two at www.imsai.net. Shipping in July. It
> >LOOKS real, but there are mostly drawings and not
> >pictures. Uses a Z80 successor CPU. Switching power
> >supply, though. $995. Still the beautiful front panel
> >that was as good as most mini's. Frankly, I find this
> >price hard to believe - too low, given the super
> >quality of the original machine and the volume this
> >might be made in.
> >
> >Does even discussing this violate the 10 year rule?
> >
> >__________________________________________________
> >Do You Yahoo!?
> >Yahoo! - Official partner of 2002 FIFA World Cup
> >http://fifaworldcup.yahoo.com
> >
>
>
>
Received on Sat Jun 15 2002 - 09:51:39 BST