XPost: sci.electronics.components, sci.electronics.design, sci.e   
   ectronics.equipment   
   XPost: sci.electronics.repair   
   From: mzenier@eskimo.com   
      
   In article ,   
   Michael A. Terrell  wrote:   
   >   
   >Mark Zenier wrote:   
   >>   
   >> In article ,   
   >> Michael A. Terrell  wrote:   
   >> >   Now tell everyone how you designed dozens of commercial products with   
   >> >the 8275. (Which was designed for 8085 based systems.) I don't recall   
   >> >ever seeing one in any hardware.  The 6545/6845 and the 5027 CRTC were   
   >> >what I've seen.   
   >>   
   >> The Intel MDS blue box system used it, if someone wants a design   
   >> example.   
   >   
   >   
   >   Was that their 8085 development system with the 8" disk drive?   
      
   Yes.  (Overdesigned slug).  There were enough of them around that somebody   
   probably has scanned the schematic and posted it on on of the document   
   archives.   
      
   Yea, there are reasons that nobody used the 8275 much.  I lucky to   
   find a 1984 databook with its datasheet on the top of my pile of boxes   
   of databooks.   
      
   Yuck.  It was one of many Intel peripheral chips from the late '70s   
   that took the wrong road.  It is a programmable video counter chain   
   (like the 6845, the one used on the IBM video cards), but instead of   
   outputting all the address bits to feed an external memory, it had two   
   internal 80 character display buffers that were loaded by program or DMA.   
   (So the driver had to babysit it, making sure it got a new line of text   
   every milisecond or so).  In operation, it only output the data byte, the   
   row counter, and some attribute bits to feed the character font ROM.   
   (Using it for graphics, at one display line per row of data would   
   either have saturated the micro's databus, or isn't even be possible).   
   It only works at the level of characters, the video serializer and   
   dot-per-character counters were external TTL.  It only ran at 2 or 3 MHz.   
      
   Mark Zenier  mzenier@eskimo.com   
   Googleproofaddress(account:mzenier provider:eskimo domain:com)   
      
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