Re: 6545 40/80 col register values

From: André Fachat <>
Date: Thu, 26 Apr 2012 07:44:09 +0200
Message-ID: <>
> Von: Rob Clarke <>

> It's still not clear to me why different register settings were required 
> for 60/50mhz versions when the PET board and monitor operates on DC. Is 
> it just to avoid minor artifacts due to ripple on the supply? Also, are 

I think it's probably the same reason as for the TV sets - interference effects with other light sources in the room. (or maybe even ripple effects on the supply too.)

> the register sets independant of the monitor size? I would assume that 
> all 80 column machines had 12" displays, but are the registers actually 
> setting the machine up for 80 columns or setting it up for a 12" display?

I haven't really made a table, because the different ROMs have many different timing values. If you look at the bottom of this page they even differed in number of screen scanlines(!) between the 40 and 80 col machines - even though (as far as I understand) the fat-40 and 80 column models had the same screen hardware (at least that's what I would do). It seems to work as long as the refresh frequency was basically correct (compensating with the scanline duration)


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