Re: 6545 40/80 col register values

From: André Fachat <afachat_at_gmx.de>
Date: Thu, 26 Apr 2012 07:44:09 +0200
Message-ID: <20120426054409.67490@gmx.net>
> Von: Rob Clarke <crock@clarke-family.org.uk>

> 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 http://www.6502.org/users/andre/petindex/crtc.html 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)

André


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Received on 2012-04-26 06:00:37

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