30 Jun
2007
30 Jun
'07
12:04 p.m.
On Sat, 30 Jun 2007, Chuck Guzis wrote:
Date: Sat, 30 Jun 2007 11:44:09 -0700
From: Chuck Guzis <cclist at sydex.com>
Reply-To: "General Discussion: On-Topic and Off-Topic Posts"
<cctalk at classiccmp.org>
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>
Subject: Re: Semi-OT: Interesting or unusual PC Compatibles?
On 30 Jun 2007 at 10:57, Chris M wrote:
We used the V40 for embedded applications many years ago, The DMA controller
is totally different than the 8257? used in a PC (in a good way, it had direct
linear 1M addressability)
We covered up the differences by emulating the 8257 (and 8255) in software --
access to DMA or 8255 I/O locations:
1. Remaps ROM to bottom to replace NMI vector with our hardwired vector
2. Generates NMI
3. NMI ISR backtracks to find I/O operation, address, and data, Then ISR does
appropriate thing with V40 DMA or our I/O bit hardware
Just why I remember this I do not know...
Peter Wallace
Fine, but does a V40 present the same
*possible*
incompatibility issues as an 80186. And for that
matter but OI NOT THE ORIGINAL QUESTION does a V20/V30
present any of it's own...
Well, if you had a decent programmer writing the code, s/he would use
a fairly standard routine to differentiate between an 808x and a V-
series chip as well as an 80286 and 80386. The code was widely
published.
You mostly saw V40/V50 for embedded use, although there were one or
two portables that used them.
Indecent programmers can go debug themselves. :)
Cheers,
Chuck