Z8002 Communications Board

Multibus I

Z8002 Multibus communications board

The work was probably done in 1983, possibly even in 1982

The photo was taken shortly after wire wrapping and possibly a static test, as there are none of the larger chips on the board. Unfortunately we don't have any later photographs, as we never thought it would make it onto the Internet!


The Z8002 base communications board was dual-ported onto the Multibus. There were eight asynchronous serial ports based on the Zilog ZSCC devices. At the time Unix systems relied on intelligent peripheral boards. The PC industry would add serial ports via shared interrupts directly onto the CPU I/O bus, resulting in poor performance and lost characters even at 9600 baud.

During the 1980s, serial links between computers and terminals were over RS-232 asynchronous links. A simple Z80 could easily handle 115 kBaud serial ports, however, the PC would take a long time to get even close without loosing characters. This was our first Z8000 based board for serial ports. An earlier board used the Z80 on STDbus.

Single Step

Z8002 single step testing on Multibus I wire wrap board


Single Step testing of Z8002 on Multibus that was wire wrapped around 1983. The single step circuit was a simple flip-flop on a small board that interfaced to the clock chip.

The flip-flop board is shown with the logic probe with the Z8002 card upside down during testing — it was easier to probe on the underside, or wire wrap side.