So, sometime during late summer of 1994 while I was in technical college, I had gotten to the point in my electronics experimenting at home where I wanted to build my own computer--something with a brain. I had a subscription to (what was then) Electronics Now Magazine, and many of the projects they featured were based on an Intel 8051 8-bit microcontroller. I was was either going to use an 8051, an 8085, or possibly a Motorola 6803. Since the Intel 8051 seemed to be a very low-level "geeky" microcontroller designed specifically for low-level signal manipulation and since I had a lot of material on it, I decided to go with the 8051.
Actually I went with an 8031 because I knew I'd be doing plenty of reprogramming to the brains of my computer, plus I didn't have a 8051 programmer and had no real money to buy one (I was in college, remember?). Well, after heavily referring to a couple schematics and the datasheets on the 8031, I had the first prototype of my 8031 computer breadborded. Chip-wise, the initial prototype consisted of:
It took me maybe two weeks to write the initial monitor code. Like I said, I didn't have an EPROM burner so I had to give my dad the EPROM and a disk with the code and he took it to work where a friend of his burned it for me.
I remember the very first version actually worked almost prefectly. I think the major bug was with the display logic, but after another revision it was up and going. Soon after this I added a download function to the monitor program, allowing me to download new code via a serial port to the second memory chip, thus allowing me to springboard off and go hog wild enhancing my monitor program without having to get EPROMs burned. The 27C32 4k EPROM was upgraded to a 2764 8k EPROM and the 6116 2k SRAM became a Dallas 1225AB-150 8k battary backed-up SRAM (I was now discovering the possibilities open to me chip-wise). Also during this upgrading I changed the clock speed from 4 Mhz. to 7.3728 MHz. to make it easier for serial port speed timing.
Anyhow, moving on... having my computer breadborded was great, but of course I wanted to see this to the logical conclusion: having it on a circuit board. This would also allow me to add some extras, like some LEDs, jumpers, and connectors. One little problem though: I had not drawn up ANY of what I had did into a schematic: I just used existing schematics to build it. Well, it took a while, but I finished the original schematic:
I found a local printed circuit board manufacturer (Wow!) and sent him a laser print-out of my schematic. Then I had my dad solder the parts onto it (with my vision problem, soldering work of this level is beyond my capabilities). Aaaaanyhow, here's the finished product!
I did have to sort-of scrounge for parts for the board. Again, I had no cash (the boards cost me $275!), so it didn't look as neat and pretty as I had hoped, but I really didn't care. This was a MAJOR accomplishment to me; my very own computer I designed, on a circuit board I designed. This big for me at the time :) It was November of 1994 and I was 20 years old.
I continued working on improving the monitor program well into 1995, when I temporarily got side-tracked from my electronics work to graduate from tech. college, move into my own apartment, and begin working full-time.
This project was picked up again later in 2000, but the details of that part of this project have been moved to here.
