Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cpqhou!randys
From: randys@cpqhou.uucp (Randy Spurlock)
Newsgroups: comp.os.msdos.programmer
Subject: Re: Vertical Beam Interrupt on VGA
Message-ID: <1990Dec12.200909.10258@cpqhou.uucp>
Date: 12 Dec 90 20:09:09 GMT
References: <2135@ccadfa.adfa.oz.au>
Organization: Compaq Computer Corporation
Lines: 28

in article <2135@ccadfa.adfa.oz.au>, bcf@ccadfa.adfa.oz.au (- Chem.) says:
> 
> I am sending this code for a friend. He can get it to work on
> an XT with EGA but not with an AT with VGA. He would appreciate
> any suggestions.
> 
> 
> <Code example deleted>

	The interrupt number picked by IBM for the vertical retrace interrupt
on the EGA must be shared with other devices and was not implemented cleanly.
Therefore on the IBM ISA VGA the interrupt line is cut, it never makes it to
the bus, i.e. you cannot have a vertical retrace interrupt on the IBM VGA. For
the same reason the line is cut on COMPAQ VGA cards...sorry to break the bad
news.

p.s. - The interrupt line IS attached to the bus on the MCA version since the
       bus was designed to share interrupt lines!


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
          - Randy Spurlock -	      |      Compaq Computer Corporation    
---------------------------------------------------------------------------
These opinions are mine...all mine... | He fired his hyper-jets and...  
just ask anyone who's heard them!     | blasted into the 5th dimension!
--------------------------------------| 
UUCP: ...!uunet!cpqhou!randys         |                     Space Man Spiff
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=