Re: 6545 40/80 col register values

From: Gerrit Heitsch <>
Date: Wed, 25 Apr 2012 17:27:29 +0200
Message-ID: <>
On 04/25/2012 07:38 AM, A.Fachat wrote:
> The 6545 cannot be switched between 40 and 80 cols, the width is
> ingrained into the hardware (80 cols require double the bandwith a 1 mhz
> 8 bit system can deliver)
> The only thing that can be done is to restrict the visible chars on a 80
> col machine to 40. Don't know the register out of my head, though.

Back when I used the 8032 there was a program called '80to40' which 
resided in the second KB of the screen memory and did some trickery to 
get the 8032 to display 40 cols. The characters were the same width as 
with 80 cols, the screen display was slightly wavy and the system would 
crash if you tried to scroll, but it was good enough to play Space 
Invaders or PacMan (written for the 3032 or 4032) on.

So there are ways to at least fake it in software to a certain degree. 
Anyone here has the 80to40 program, taking that apart should give all 
kinds of hints how to handle the CRTC.

It was fun to watch... You loaded it, then ran the loader which would 
fill the lower part of the screen with garbage and then jump into it, 
the screen would go blank for the moment, then return with a 40 col 
display centered in the middle of the 80col screen and a READY. prompt.


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Received on 2012-04-25 16:00:27

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