Mark Zenier wrote:

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.


It's one of the few things I don't miss from the rental warehouse I
lost when I got sick, and couldn't work for two years.


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.


I have a databook with it as well. It looks like you were to buy
their development kit to learn to program all the registers. It's no
wonder that it wasn't popular.


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.


It was covered in the CRT Controller Handbook, but I misplaced my
copy long ago.