Re: 6545 raster effects (Re: 6545 40/80 col register values)

From: André Fachat <>
Date: Thu, 26 Apr 2012 21:14:12 +0200
Message-ID: <>
> Von: "Marko Mäkelä" <>

> Can the 6522 VIA generate interrupts? Even if it cannot, you could use 
> the VIA timers to simplify the cycle-counting.

Yes, the VIA can do interrupts. 

> On the PET, if there is no readable raster line counter in the 6545, I 
> guess you would need a trick that uses the IRQ line for determining when 
> exactly the vertical blank interrupt is being triggered. Then, you would 
> set up some sort of a delay loop in the "main program" and wait for N 
> more vertical-retrace interrupts to eliminate the horizontal jitter.

No, the 6545 does not have a readable raster line counter. In fact none of the registers you can write to can be read (IIRC)

And I have done that IRQ handling in my test programs at - on the vertical irq set the VIA timer and then on VIA interrupt change the CRTC registers.


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