When people pull out their old KIM computers, one of the first things they'd like to do is plug into an RS-232 terminal or PC and run the debugger from there rather than the KIM keypad. Unfortunately, the KIM's TTY port is a 20 ms current loop interface designed for connecting to teletype terminals, which were readily available in the 1970's.

So began my next expansion board!

This board plugged into the Application connector, so I didn't want to preclude the use of all the other signals, which meant they had to come to usable connectors organized into some logical groupings.

DSC00273

Here is what the card has:

  • RS-232 conversion for the 20 ma current loop. Comes to a DB-9 female connector.
  • Easy power connector for +12, +5 and ground.
  • Two jacks for connection to an audio tape recorder.
  • Jumper to select AUDIO HI or AUDIO LO output to the cassette jack.
  • Jumper to select keyboard or TTY for KIM monitor operation.
  • Jumper to either force DECODE ENAB low or use external logic to drive it.
  • PA and PB I/O bits brought to a dedicated header.
  • DIP switch to select which K1-K4 lines (or all) go to a dedicated memory select header.
  • Memory and I/O decode header for easy memory or I/O expansion.
  • Header for easy connection to my 4K memory expansion board.

The design is not complicated at all and can obviously be heavily modified for what you want to do. You can certainly build one yourself. Here are the complete schematics. Many people only care about the RS-232 level conversion, so they are free to build just that part of the board. Since I wanted to have all the features on a single board and look neat at the same time, I had PC boards made. They're professionally etched and double sided, but do not have a silk screen. I sell blank boards and fully assembled versions. There are no exotic components.

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