20 Feb
2009
20 Feb
'09
9:17 a.m.
On 19 Feb 2009 at 19:27, Les Hildenbrandt wrote:
There was also the NEC V20, which was pin for pin
compatible with the
8088. It was a CMOS part. There were a few instructions that the V20
executed in fewer clock cycles than the 8088 (multiply comes to mind),
causing some motherboard vendors to install a V20, and the sell a 10mhz
motherboard as a 12mhz motherboard.
The problem with the V20's 8080 emulation was that it was buggy (I
have a few MicroNotes on the subject and can even claim to have
discovered one of the bugs). For me, the V20 ultimately proved to be
more useful by providing many of the 80186/286 instructions that the
8080 lacked. Use of a V20 with an 8087 NDP could also create
problems of its own, so the added functionality was not without its
own problems.
It's also worthwhile to mention that the V20/30 has instructions that
none of the Intel x86 members has, such as packed BCD string
arithmetic.
I believe that the emulation mode features extended to the V40 and
V50 chips also. At least that's what my databook claims.
Cheers,
Chuck