It can be argued that if it uses code not executable on an 8080, it's not
really CP/M-80 software. If it runs the 8080 that's supposed to be in an
IMSAI, and supports the CP/M/IBM-3740 8" SSSD diskette format, it's close
enough. The problem there is that the IMSAI FDC doesn't, IIRC, use
soft-sectored diskettes.
If you run an 8080-mode V20, you can run a BIOS written in 8086 code, which
may offer considerable advantages over the 8080-only BIOS. What's more, if
you do that, then you can incorporate ISA-bus cards into your S-100 system
with an adapter, which can make development of a comfortable computing
environment much easier. An example might be the video circuitry and
keyboard. If you put an 8-bit ISA monochrome board on an S-100 card, you can
then use the driver code in the PC BIOS (as in the printed listing in the Tech
Ref) and you can use it pretty much independently of the CP/M system BIOS,
since it will be called from the code to which control is transferred whenever
there's a BIOS call. All the CP/M BIOS has to do is call the code that
switches to native mode before interpreting the parameters of the call.
I've looked long and hard at this, having wanted to use a V50 (16-bits,
enhanced execution unit, integrated peripherals, DMAC, PIC, UART) in the same
way. Mounting a couple of 8-bit ISA cards on an S-100 board is quite
straightforward, and the signals seem to work out quite well, too. The
combination I'd use would be an 8-bit monochrome display board and an 8-bit
HDC.
Dick
----- Original Message -----
From: "Hans Franke" <Hans.Franke_at_mch20.sbs.de>
To: <classiccmp_at_classiccmp.org>
Sent: Wednesday, April 10, 2002 8:27 AM
Subject: Re: Native CP/M
> > > Well, usualy this doesn't work, because of the different CPUs
> > > (I assume we are talking about CP/M80 - CP/M86 will of course
> > > boot on most classic PCs). The only way beside Emulators under
> > > DOS/Win, and rare coprocessor boards is of course the NEC V20.
>
> > > A V20 is for all PC/PC-XT machines a must, because of about
> > > 10% faster execution (the V20 core is build like the 186/286).
>
> > The problem with the V20 (and the V30, which IIRC is the '8086' version)
> > is that you only get the 8080 instruction set. And while CP/M will run on
> > an 8080, a lot of the more recent CP/M software needs a Z80.
>
> Yep, you're right. It did quite work well with my
> software. And IIRC he was talking about software
> development for an IMSAI, and that's and 8080, if
> not modified with a Z80 CPU board - which again
> would be no IMSAI anymore :) So a V20 with the
> 8080 mode is adequate.
>
> Gruss
> H.
>
> --
> VCF Europa 3.0 am 27./28. April 2002 in Muenchen
> http://www.vcfe.org/
>
>
Received on Wed Apr 10 2002 - 12:47:39 BST