11 Mar
2003
11 Mar
'03
1:06 p.m.
On Tue, 11 Mar 2003, Hans Franke wrote:
There ARE some differences. It'll drop in as a replacement on a
5150. But on a Gavilan, which uses an 8088, there are modifications
required. Uncle Roger has my old Gavilan files, which include a Gavilan
document detailing the modifications needed.
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.
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.