XPost: alt.lang.basic   
   From: bruce#fanboy.net@127.0.0.1   
      
   In article ,   
    "R Flowers"  wrote:   
      
   > I'm not well versed in the hardware, either, but my guess would be that   
   > Radio Shack used 'helper' chips that drove the video, thus not having to   
   > rely on so much processing power from the CPU. The TS 1000 and its ilk were   
   > made to be as cost effective (ie, cheap) as possible, so the designers   
   > decided that the CPU would have to drive everything. (That's speculation on   
   > my part.)   
      
   The TRS-80 did not have a "video chip".  It had discrete TTL circuitry   
   to handle the video output.  However, bus contention between the CPU and   
   the video circuitry was always decided in favor of the CPU.  The video   
   would be blanked during these periods.  As there was no way to determine   
   when the video was in a sync state, any CPU access of the video memory   
   would cause black streaks of "hash" to appear all over the screen, and   
   there was no way to avoid this except by avoiding unnecessary writes   
   (don't rewrite data to the screen memory when it's already there).   
      
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