Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uunet!mcsun!ukc!dcl-cs!gdt!ccsdra
From: ccsdra@gdt.bath.ac.uk (Dave Allum)
Newsgroups: comp.sys.ibm.pc
Subject: Re: 512K VGA Programming
Message-ID: <1990Jan10.130323.9810@gdt.bath.ac.uk>
Date: 10 Jan 90 13:03:23 GMT
References: <1990Jan7.023913.5900@IDA.ORG>
Reply-To: ccsdra@gdt.bath.ac.uk (Dave Allum)
Organization: BUCS, University of Bath, U.K.
Lines: 22

In article <1990Jan7.023913.5900@IDA.ORG> roskos@IDA.ORG (Eric Roskos) writes:
>Does anyone have experience with writing to a 512K VGA in the 8-bit
>pixel modes?
>
>Clearly you can't just write to it sequentially like in mode 13H, since
>there isn't enough of the address space available.  But I don't see any
>sort of "bank switching" register on the VGA (at least, not in the
>Ferraro text). 
>
>   ... other stuff deleted ...
>

The reason there is no bank switch register is that IBM only believes in
256K VGA which doesn't require any bank switching for the supported display
modes.

The manufacturers of the super VGA cards with extra modes and 512k provide
bank switching in various ways which involve differing address calculations
and writing (or, in some cases, reading and writing) one or more i/o ports
on the adaptor. Unfortunatly there is no single method and what you have to
do depends on the chipset used by your VGA card. The best bet is to read the
programmer's manual for your particular card.