For those who wonder what that jumble of letters and numbers mean, it is the part number of the central processor from very first computer I built/programmed back about 1979. A CDP1802 is much like "486" or Pentium is to Windows PCs today (the "brain"). It holds a special place in my heart and when I wanted to setup a domain for myself, it seemed like a good starting point (all the good domains like "body-crevice.org" were already taken).
As a kid, I had been building things from peoples discarded appliances, TV, radios and occasional parts I actually bought (most of the stuff was fished out of garbage cans and from the local dump) for most of my childhood and was pretty adept with electronics (digital and analog), but never a full scale computer.
A friend of my moms had recently "upgraded" from a CDP1802 based computer to a new Apple ][. Being reasonably nice folks, they gave me their "Elf II" (a CDP1802 based single board computer sold as a kit from a company called Neutronics in Connecticut). I was excited but at a loss as too where to start. As was my style when dealing with unknowns , I immediatly tore it apart. It worked for a few weeks, until my curiosity and my (at the time) limited experience with soldering delicate tiny parts did it in.
However, within a few weeks of that, I had acquired all the parts I needed (and scavanged the rest from my DOA's Elf) to construct my own computer. I used the RCA CDP1802 processor manual (a fairly technical manual designed as a reference, not a tutorial) and got the thing working in about 2 months. Learning to program (beyond trivial things) took a few more months before I was fully versed in the intricacies of the CDP1802 and the general concepts of programming in general.
This all led me to the rest of my life (as abstractly documented in my home page). I spent nearly all my time and most of my money on this thing. I built hardware, wrote programs, wasted my formative junior and senior high school years and basically hid in the basement with this thing until, after aggravating the high schools computer science teacher and system administrator, got a real job programming computers (PDP 11's running RSTS/E). Then I had some serious money to dump into my computer, but less time (pesky boss wanting to see me in the office before noon).
Lest you think this was anything like what most folks have today (computer wise), this machine at first had a 16 key hexidecimal keypad, a couple of toggle switches, a two digit numeric display and a single LED. It had a whopping 256 bytes (that is 1/4 KByte or 1/4096th of a megabyte) and no way to save anything permanently (no floppy disk, hard disk, tape drive, etc). It was still an upgrade from other computers at the time that used rows of toggle switches to enter data (which is very cool, but really tedious).
You wrote the programming in an assembly language that looked like this
7B
7A
30 00
That was a program that would turn the LED on, then turn it off, then loop back to the start and do it all. That was pretty exciting stuff! Eventually I was able to expand the system to allow me to store programs to a cassette tape player, talk to a terminal (which I had also built) and on one great day, added 4KB of memory to the system. At the time, I couldn't imagine how I would be able to ever fill all of it up.
For those who know what the CDP1802 is and are disappointed that there is nothing of real value here, please just hold on a bit. While I don't plan on making anything like an exhaustive website/reference for the CDP1802, I do plan to colllect a a number of links and offer at least a common jumping off point for folks interested in the CDP1802 or just fondly remembering their earlier computers.
If you have any ideas or CDP1802 related resouces you'd like to see included, please feel free to mail me at gerry@cdp1802.org
Last Updated April 16, 2000