Theo Verelst Z80 System Page


To give the synth on my other pages Midi and automated and programmable controls, a microprocessor is desirable. An of-the shelf card or PIC processor could do, but I chose to (re-) do a Z80 design, and give it loads of IO lines, and the properties needed to do all inds of prototyping.

System Overview

Below is a picture of (one of the) prototypes, showing de CPU-card, programming hardware, and the keyboard.

The properties of the system are: Z80 CMOS CPU (at 2 to 40 (!) MHz, at least one of the prototypes ran at that speed), a battery backed RAM (currently 8Kbyte), display and keyboard interfaces, and the rest of the (random) logic to make the system work.

Display Unit

Top view of the display unit:

Except for the adaptations in the lower right which were to dispable a power surging archaic static ram , and to make a different, simpler, interface, all parts were soldered about 15 years ago, and were in fact quite advanced for those days, since the applied CMOS parts were already very low power, so the whole display unit can run a fractions of a milli-Amp, except for the LED segments.

Bottom view of the display unit:

Program Examples

I've done some simple programs on this prototype to test memory access, stack handling, and basic IO,  followed by a program to drive the display unit described above. basically the display's are addressed in a row, and display a message prepared in a 16 byte long memory image. By shifting the memory image, a text can be scrolled.


I've laid hands on a set of 5x7 segment LED displays, that I'll use to make a display with better alpha-numerical capacities, at the expense of more power usage and hardware. As a display unit for the synthesizer and other audio equipment, this seems a cost effective and very desirable option, since it beats LCD's by far in readability and speed.