CDP1802,1977-1982


This page is made in response to a request received February 3, 2017:

"On behalf of theRCA COSMAC CDP8012 retro-computing hobbyist community, I would like to request more info about the computer you built, and your input device on this page. Most of us have an interest in anything 1802 and I think people would find it interesting if you could expound on what you have, with more images if you have them, and mention the work you did in as much detail as you can."



It's been near forty years since I have looked at anything 1802, so I was surprised and happy to learn it still has fans. It was the perfect intro to embedded computing and machine-language programming. RCA's VIP documentation, along with the ELF projects in Popular Electronics magazine made the technology accessible to low-budget geeks. Together we learned to make rasters on crts -and even did some primitive vector drawing all in machine code as hex digits on the 8-bit bus. Mass storage was on audio cassette -and it often seemed magical when it all worked.
The device used to enter the machine code was the Digitport described in an article (1980) I had hoped to see in print, but which was deemed "a little odd for our readership" by the editors. Here's a copy. My 1802 systems were wire-wrapped and constantly changing, but stayed within the definitions of the ELF. It was nice to sit in a comfortable place with a clipboard (that's a board, with a clip to hold paper) under the right hand, the Digitport in the left, a gin and tonic nearby, pumping machine code into a massive 2K of RAM. One project was to make an "os" of sorts, and led to an article that did get published in Popular Electronics.
These images are scans of the original code from the clipboard, -the work of the right hand as the left hand enters bytes by digitport.


This might look a bit primitive, but such a direct relationship with the bits was very appealing and I continued to use this input device as the Z80 elbowed the 1802 off the bench, and only after a couple years gave in to qwerty and Cp/M and assembly language. Maybe 2017 is a good time to revisit and upgrade the digiport --with a small PIC and a serial interface...
So that's what I have of 1802 history in my shop. Thanks for the inquiry, -it triggered some pleasant memories.

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