
Aus http://www.atari-forum.com/viewtopic.php?t=5677

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You have luck :-) I've made the sources now available. You can download them 
under http://wwwbode.cs.tum.edu/~acher/blowup ... ources.tgz 

They were developed with Pure-C. They contain a lot of german comments (some 
of them really nonsense ;-), but they should be understandable with a little 
bit bablefish... 

Regarding the hardware: The Hard 1 was a simple 50MHz quarz oscillator 
feeding the pixel clock input. The only trick was a resistor from the clock 
signal to ground (depends on the oscillator, about 120 to 220 ohms, if its 
wrong you see white or black streaks). 

The Hard 2 had a variable pixel clock (33-55MHz), but contained no "real" 
PLL. It was a VCO (NE564), its control voltage was generated by a CMOS 
sample and hold circuit (CD4007) and a large foil capacitor. The paddle port 
provided the up/down control of the voltage. There was a continous software 
feedback loop measuring the vertical blank frequency and adjusting the 
voltage accordingly. Sounds like an ugly hack, was ugly, but worked quite 
good ;-) The only trick was to stabilize the 5V from the Falcon, which was 
done by a TL497 switch converter and a 78L05 linear regulator. 

-- 
 Georg Acher, acher@in.tum.de 