38dbf7dc   
   From: joe@user.com   
      
   "GrantH"  wrote in message   
   news:e859639c-51c8-4d98-935d-237f4b179534@d1g2000hsg.googlegroups.com...   
   > Hello - I just purchased a graphics card add-on for the Model II   
   > TRS-80.  It comes with the card, 2 ribbon cables with card-edge   
   > connectors which terminate w/IC plug-ins, obviously to replace IC's on   
   > the normal video card.  The documentation includes only discussing   
   > grahics BASIC, programming in other languages, etc.  There's a bit   
   > about having my qualified Radio Shack technician install the card, no   
   > instructions on the installation.   
   >   
   > Wondering if anyone knew the hardware installation step?   
   >   
   > Grant   
      
   OK, I HOPE I remember this right...   
      
   What you do is open the card cage (power off, of course!  And make sure   
   you discharge yourself as well!) and remove the video card.  You will remove   
   the video card.  You will careful remove the 6845 chip and the ROM   
   chip from your video card, and move them to the graphics card.  Then you   
   will plug in the cables that came with the graphics card into the sockets   
   where you removed the 6845 and the ROM, and carefully route the cables   
   to the graphics card.  Be careful of  pin '1'!   
      
   Put the video card back into the card cage with the graphics card in the   
   adjacent slot.   
      
   Do NOT leave any empty slots between cards in a Model II card cage, as   
   not all signals are 'in parallel'.  The interrupt enable signal 'daisy   
   chains' through   
   cards, and even if a card doesn't use the signal (like the memory card) it   
   still passes the signal through.   
      
   If the machine video works as normal when you power back up, you have it   
   working correctly.   
      
   The graphics card works by intercepting the video address signals and doing   
   an XOR of the character data with the graphics data.  With the graphics all   
   set to '0', then the screen looks normal.  Any area that sets graphics '1'   
   bits   
   will be inverted.  That is, black becomes white and white becomes back.   
      
   If you get noise and tearing of graphics, then the LS chips that drive the   
   address lines to the RAM on the graphics board need replaced with S parts.   
   (LS technically could drive 10 standard loads, but there were 16 RAM   
   chips.  Most boards worked, but some needed changed.)   I think the   
   boards were all changed in production but a few might have gotten out with   
   LS parts.   
      
   Mike   
      
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