XPost: sci.electronics.design   
   From: invalid@invalid.net   
      
   >> So, how critical *is* this frequency?   
   >   
   > it's hard to say. it depends on the monitor.   
   > try a 9MHz crystal it's within 2% of the target , you might need to tweak the   
   > vertical and/or horizontal hold adjustemnt on the monitor.   
      
   When I vary the sig. gen. I used to simulate the crystal in this circuit, the   
   output video signal doesn't vary at all (sync pulse timing stays the same).   
      
   Therefore I presume that video timing is determined by the other crystal (6   
   MHz) that is running the 8085 uP on this antique board.   
      
   So I also presume that this 8.867 MHz crystal drives the dot clock (shifting   
   bus data into the 8275 CRT controller IC).   
      
   Is the 8.867 frequency critical at all? Since it doesn't control the video   
   sync pulses, etc., what effect will it have on the (ASCII text only) video   
   display?   
      
   Thanks,   
   Dave   
      
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