Clone Computers

The TRS-80 was a good computer in it's day. It had BASIC in the ROM which meant that it booted VERY quickly.

It also had one big drawback - the power switch would sometimes work itself into the Off position, usually just before a CSAVE operation.

I decided that I could build a better one, and be able to fix it myself if I mada a mistake while interfacing it. At the time, one of the bigger computer magazines stated that "It is impractical to build a computer from scratch". Sounds like a challenge to me. I studied the TRS-80, and decided that I could seriously reduce the chip count by using the newer octal bus driver chips, and static RAM chips. The next big obstacle was the character generator chip, so I designed my own with a 2716 EPROM. All I had to do was figure out how the bit patterns were stored, and write out the HEX codes to burn into the chip. The first one almost worked - I omitted the top bar from the letter "T". No problem - I had CSAVE'd the data. Just change one line and burn it again.

It was a good learning experience. If it worked the first time, I wouldn't have learned much.


Here is Clone 1. With one exception, they were all wire-wrapped. This picture was taken just after I got it working right. In spite of not having a disk drive, or color, or lower-case test, or hi-res graphics, or RS232, or more than 48K of RAM, I did a lot of stuff with these computers.

I had a MIDI interace, a custom multi-port musical keyboard interface, several EPROM burners, speech synthesizer, plotter, guitar synthesizer, EPROM emulator, and EPROM loader.


Clone 2

This version was built in a roll-around cart. On the left is the cassette recorder (yes - they did work much better than some people claimed - you just need to use GOOD tapes), a 4 inch video monitor, and the TRS-80 Quick Printer.

I used this computer one Halloween to run the Dancing Demon. If you haven't seen it, it displays a little dancing figure which can pe programmed to do a variety of dance steps. I set it up to run at the same tempo as the Ghostbusters theme which I piped out onto the porch, and ran the video output through a 14 inch amber monitor. The kids went nuts over it, mostly because IBM graphics hadn't been seen by the general public. It was also long before Elvira's time, but that's a different story.


Here's tht Clone 2 with the top open.

The Clone 3 computer was a general purpose unit used for interfacing experiments.

The Clone 4 computer was built into an old terminal. This one was most often used to run the Casio CZ-101 synthesizer through the MIDI interface, and a regular Casio keyboard through a custom interface, using 49 opto-isolators.

Clone 5 was built in a cabinet which used to house a disk drive test unit. This was the first true portable I built. It also has an EPROM socket which allowed me to load EDTASM instantly.

This is the the fourth EPROM programmer I have built. The first one was a standalone which had thumbwheel switches for the data input, and a binary counter for the address input. The second one was memory mapped to the TRS-80. I don't remember the third one, but this one was able to program from another device, or from the TRS-80 memory. It also featured separate sockets for the different EPROM types.

The fifth programmer plugs into a parallel port board on the XT/AT computer.

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