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Early Low-Power Z-80 Microcontroller

2016/04/28

In the mid 1980's I was a partner in a technology startup that was developing a low-power data recorder for engineering and resource management applications. My part of it was to write the firmware for the device.

Along the way, I became interested in the possibilities of low-power computing and decided to design a general purpose microcontroller to give us a second product we could market at lower cost.

This rough-looking device comes from a phase of my career where I attached little importantance to the physical appearance of my prototypes.

It uses a CMOS Z-80 processor clocked at 2 MHz with a crystal oscillator, I beleve 4KB of CMOS static RAM, and a 4KB EPROM. The logic chips that glue it all together are 74HC00-series high-speed CMOS. It has an expansion bus capable of driving a couple of programmable I/O devices, as well as 8 bit input port and an 8 bit output on-board. The on-board ports are intended to configure the device and to display its status.

74HC logic was considered pretty hot technology when it first appeared. You can see one of the advantages of using it in the picture above: There are almost no decoupling capacitors on the board, yet it runs glitch-free at 2MHz because of the parsiminous power consumption of the ICs.

It's broadly similar in concept to something like an Arduino. I would hasten to note that the Arduino, or almost any other present-day microcontroller, has about eight times the speed and resources of this little machine but for 1985 it was fairly respectable.

The support requirements are a little exotic by today's standards.

You'll need a computer with either a Z-80 or an 8080 assembler to generate machine code, and an EPROM programmer to burn the code into the board's read-only memory. Flash memory and EEPROMs were just a twinkle in some engineer's eye in the mid 80's. I used an Apple II clone equipped with a Z-80 card, CP/M 2.2, and a Canadian-made EPROM programmer from a Toronto-based company called Gladstone Electronics to program the thing.

The prototype is built on something called Vero Board, which many people of a certain generation will be quite familiar with. Vero Board was a circuit prototyping board made made in England of a phenolic material resembling dried yak dung with a generic grid of conductors on the wiring side. Using a piece this size for a project was not the best idea because the stuff was quite flexible.

That aside, it's still fully functional after all these years.

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