XPost: sci.electronics.design   
   From: jasen@xnet.co.nz   
      
   On 2013-02-14, DaveC  wrote:   
   >> So I also presume that this 8.867 MHz crystal drives the dot clock (shifting   
   >> bus data into the 8275 CRT controller IC).   
   >   
   > Or rather, loading 8-bit bus data into a parallel-to-serial shift register   
   > and then into the 8275 CRT controller.   
      
   usually the CRTC manges the raster size and does its own   
   data fetches...  I'm not familiar with the 8275, but all   
   the CRTCs i've encountered had internal counters to   
   determine the sync rates and sync pulse widths. from the   
   pixel clock that crystal may be doing something else,   
   colour-burst  perhaps.   
      
   Is this circuit used with some sort of genlock - text over video ?   
   if so then the crystal frequency may be critical.   
      
   perhps feed an FM signal into where the crystal goes and   
   probe around to see where it's going.   
      
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