> > > I might be able to use the 8088 docs. The V20 is *supposed* to be a drop-in
> > > replacement, but IIRC it needed some (minor) BIOS alterations to get it to
> > > work properly in PCs when the 8088 was swapped with a V20.
> > Not that I know off. The V20 did behave exactly like an 8088.
> > At some point I did use them on every PC and XT I could. The
> > additional speed was quite cheap. The only time I couldn't
> > use a V30 was in the Siemens PC-MX, a small 8086 Unix box.
> 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.
Well, that's eactly the 186 behaviour. Now considering that the
timeing was also exactly like 186 (or real mode 286), and the
instruction set is the same, I still think NEC just used the
186 (188) core as template for the V20/V30 - Considering that
V40/50 where like the 186 with integrated perhipherals, you
may considere it as a two step knock off...
Gruss
H.
--
VCF Europa 4.0 am 03./04. Mai 2003 in Muenchen
http://www.vcfe.org/
Received on Wed Mar 12 2003 - 05:23:00 GMT