Planning the COLLIER-1

Jan 31, 2013

Hi all, I’ve had a long-standing (and by this I mean “since around the age of eleven”) desire to build a computer from scratch.

I’ve finally planned some computer-weekends, and have started collecting the raw materials for a computer. The first decision that I had to make was about the processor to use.

I’ve been able to program x86 assembly for a long time, so I did consider an 8088, 8086 or similar, but the multiplexed addressing and data buses looked a bit complex. I did, however, buy an 8085, simply for the weirdness factor - it would be great to do something other than “yet another homebrew 6502 box”.

For a while I looked at the Z80, but that’s pretty common too, so I’ve settled on using the 6809, a latecomer to the 8-bit processor market, but apparently widely respected. Bill Gates, for instance, was a big fan. There’s no multiplexed address bus, and while it’s not been used by a lot of people, there are successful reports of people building great home systems with it. This chap, for example.

I’ve ordered my 6809, so the next step will be to test it out on a free run. I am also going to be building the IO hardware off the back of a Parallax Propeller, to begin with (but not in the end - it’s cheating!), so that’s another task to be dealt with soon.