With a Cherry On The Side – Episode One


It’s kinda strange to be doing this in April instead of January, but as the RetroChallenge schedule has changed, it is time to get my plan together.

Inspired by previous attempts, my modest entry to RetroChallenge this time is to interface a PS/2 keyboard to a 1987-vintage 68hc11 micro-controller; enough to at least read the scan-codes and twiddle the keyboard LEDs. And to write it up, hopefully illuminatingly, here.

Chips Down

Of course, thar be some equipment needed, and here is what I have gathered already…

Adapt-11 SBC close-up

The Adapt-11 is a 68hc11-based SBC. In fact, it is not much more than a 68hc11 adapter. Apart from the MPU, the board contains:

  • 8MHz crystal oscillator can connected to the MPU via a couple of capacitors and a resistor.
  • MAX-232 serial-port voltage-level shifter, connected directly to the MPU serial-port pins.
  • 5V voltage regulator.
  • Manual reset button connected to the MPU bidirectional-reset pin via a pullup resistor.
  • a pair of two-position switches connected directly to the MPU “run-mode” pins.
  • a very small handful of capacitors and resistors, and a power LED.
  • a pin-header providing external access to the MPU pins.

So, as you can see, basically just a mounting adaptor for the MPU.

A terminal for the Adapt-11

To make sure the 1980s MPU chip was working, I connected a terminal emulator (PuTTY running on an 1999 HP OmniBook 500) to the MPU serial-port…
Adapt-11 Lives!

and you can see it running the Buffalo Monitor from on-chip PROM. What’s more, I recognise that program code at address B600 in the on-chip EEPROM – basic chip-initialisation code I wrote when I was playing with this particular chip in my Motorola EVB SBC two years ago.

Observant readers may notice something unusual about running code from on-chip PROM on this particular model of 68hc11 chip, but that’s a subject for next time. Stay tuned!

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