V20 trivia (was: WTD: NEC V20 Hardware Manual, IBM PC schematics

From: Peter C. Wallace <pcw_at_mesanet.com>
Date: Wed Mar 12 22:37:00 2003

On Wed, 12 Mar 2003, Fred Cisin (XenoSoft) wrote:

> > > > Not that I know off. The V20 did behave exactly like an 8088.
> > > Besides, it wasn't a completely Bug-For-Bug replacement. NEC failed to
> > > implement some of the quirks of the 8088. For example, if an interrupt
> > > occurred during the execution of an instruction with a double prefix, the
> > > NEC would continue, but the intel would drop one of the prefixes when
> > > resuming.
> > > REP MOVSB DS:[SI] DS:[DI]
> > > will resume with a V20, but with an 8088 will only do one more rep after
> > > an interrupt.
> On Wed, 12 Mar 2003, Hans Franke wrote:
> > Well, that's eactly the 186 behaviour. Now considering that the
>
> Not MY experience. The 386 is the first Intel that I'm aware of that
> fixed the double prefix bug. But NONE of the NEC v series had that
> bug. (ONE way to tell whether the current chip was Intel or NEC)
>
> > timeing was also exactly like 186 (or real mode 286), and the
> > instruction set is the same, I still think NEC just used the
>
> Did the V20 have the INSB/INSW/OUTSB/OUTSW instructions? (present in
> 80186/80188, but not 8086/8088


Yep... We made use of them in the V40 that we used for many years in embedded
Stuff. Plus the V40 has (had?) a really nice DMA controller.


snip...

Peter Wallace
Received on Wed Mar 12 2003 - 22:37:00 GMT