Path: utzoo!mnetor!uunet!husc6!rutgers!iuvax!bkliewer
From: bkliewer@iuvax.cs.indiana.edu (Bradley Dyck Kliewer)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Two Monitors on a PS/2?
Message-ID: <8077@iuvax.cs.indiana.edu>
Date: 21 Apr 88 19:31:37 GMT
References: <206900111@prism> <7955@iuvax.cs.indiana.edu> <3892@killer.UUCP>
Reply-To: bkliewer@iuvax.UUCP (Bradley Dyck Kliewer)
Organization: Indiana University CSCI, Bloomington
Lines: 33

In article <3892@killer.UUCP> chasm@killer.UUCP (Charles Marslett) writes:
>Actually, the PS/2 BIOS does have a set of calls to support a VGA installed
>in a system with a VGA already present (the hardware I/O addresses are 0x03C3
>and 0x4??? -- don't remember that one right off) -- the scheme only supports
>one add in card and the one motherboard video, but at least on the model 30
>it does work (we have installed STB VGA's and switched back and forth from
>motherboard to/from add in card).
>
>I am currently working on a new product that had 4 (expandable to 8) EGA's
>in a single system (say WHY please!),  using the same scheme.  So it is
>not only workable, but rather easily extended.
>
>Charles Marslett
>chasm@killer.UUCP
>...!ihnp4!killer!chasm

I was thinking in terms of having all memory addressable simultaneously.
Yes, you can disable one VGA (put it in sleep mode via register 0x0094)
and then use the other.  Register 0x03c3 is used to enable or disable the
display -- this register is not disabled by the sleep bit.  Since I have
never done this, I am curious; what happens if you have two VGA's and
disable the display -- do both go blank until re-enabled?

It is a different technique than most people are used to, however (the 
Monochrome adapter and CGA, or color EGA, use different addresses for video
memory, and you need only write to the approriate address).

Orchid has even come out with a VGA for the PS/2 (I saw the ad a few days
ago), so it should be possible to extend this to the Model 50, 60, and 80.

Bradley Dyck Kliewer                Hacking...
bkliewer@iuvax.cs.indiana.edu       It's not just an adventure
                                    It's my job!