8008guy
Veteran Member
I have a xerox 820 mainboard that I am working on. The video output is designed for a ttl monitor. Can anyone recomend a suitable monitor that will work?
Len
Len
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Modern option to replace a ttl monitor
- Thread starter 8008guy
- Start date
tipc
Banned
not without knowing it's horizontal and vertical sync frequencies.
That mobo resides inside the monitor. It may seem redundant to acquire another motherboard/crt combination. I'm thinking some sort of homebrewed converter to output ntsc video.
That mobo resides inside the monitor. It may seem redundant to acquire another motherboard/crt combination. I'm thinking some sort of homebrewed converter to output ntsc video.
smbaker
Experienced Member
Perhaps use an MCE2VGA? Though you might have to adjust the code if the frequencies are not what it expects.
8008guy
Veteran Member
I did find the specs in a manual on bitsavers. It does appaer reasonably close enough to ntsc to use a combiner. It'll be a month or so before I get the video section populated to look at on a scope.
Thanks for the repiles.
Thanks for the repiles.
gekaufman
Experienced Member
Remember that the Xerox 820 was essentially the same circuit as the early Kaypro or Digital Research Computers "Big Board". There is probably lots more information about monitors in either of those - and the Big Board manuals are especially useful. All are pretty easy to find on line (or PM me and I can email you copies).
http://dunfield.classiccmp.org/miscpm/bbdiags.pdf has the schematic for the big board, and there is a part of the circuit that creates composite video from the individual ttl signals that would be easy to copy.
MicroCornucopia was a dedicated journal and was a wealth of knowledge (especially the early issues). https://archive.org/details/microcornucopia
- Gary
http://dunfield.classiccmp.org/miscpm/bbdiags.pdf has the schematic for the big board, and there is a part of the circuit that creates composite video from the individual ttl signals that would be easy to copy.
MicroCornucopia was a dedicated journal and was a wealth of knowledge (especially the early issues). https://archive.org/details/microcornucopia
- Gary
I did find the specs in a manual on bitsavers. It does appaer reasonably close enough to ntsc to use a combiner. It'll be a month or so before I get the video section populated to look at on a scope.
Thanks for the repiles.
8008guy
Veteran Member
I have compared the schematics with the BB. There are some differences. The 820 leaves out the video combiner as it doesn't create a composit signal. It also uses a 10.7ish mhx xtal rather than the 14ish mhz xtal of the bb. They modified the reset circutry on the timing chain. I need to sit down and understand how that effects things.
Remember that the Xerox 820 was essentially the same circuit as the early Kaypro or Digital Research Computers "Big Board". There is probably lots more information about monitors in either of those - and the Big Board manuals are especially useful. All are pretty easy to find on line (or PM me and I can email you copies).
http://dunfield.classiccmp.org/miscpm/bbdiags.pdf has the schematic for the big board, and there is a part of the circuit that creates composite video from the individual ttl signals that would be easy to copy.
MicroCornucopia was a dedicated journal and was a wealth of knowledge (especially the early issues). https://archive.org/details/microcornucopia
- Gary