Former Zilog Engineer Talks Prototype Survivor

I recently had a chance to ask a former Zilog engineer a few questions about his remarkable single board prototype I had just acquired for the C.C. "permanent collection".  This single board computer provided a 16K reference design for 8-bit home computers and arcade games.

Zilog is one of the few platforms in the world where vintage collectors and active developers lust over the same toasted sand.  The QUIP packaged Zilog Z8-02 made in 1979 commands $500 because it is not only highly collectible but in short supply for a replacement part.

Super-optimized ZNEO covers much of the same territory Intel's 8086 did back when the Battle of the 80's was raging but outperforms modern RISC.  The company's current Icebox dev tools owe their existance to a prototype single board computer created in 1978 to test the 4MHz Z80A.

According to the retired engineer, "When CPU performance elevated from 2.5 MHz to 4 MHz, this hand-built wire-wrap prototype was built to verify the design improvements and validate the functionality under in-circuit emulation.

The emulator plugs into the CPU socket, providing the engineer a portal into the operation of the hardware and software.  A boot prom allowed serial port access with an improvised DC-DC converter modified to provide the bipolar RS-232 output voltages.  At the time, emulators were the best way to check out new hardware as they pioneered the debug tools now taken for granted.

Placed on the included display stand, this respectable and rare relic speaks to the heady days of the Microprocessor Revolution --  visible proof that the March of Progress found continuity through these kinds of steps -- prototype design and implementation for validation (prior to simulators).

History's critical path temporarily vectored right through this particular prototype board which spearheaded the drive for next-level performance in the competitive 8 bit CPU marketplace dominated by Intel and Zilog.  It proved the process improvements to NMOS IC fabrication with 4" wafers could reduce the manufacturing costs as well as increase the raw processing bandwidth.

Z80 Verification Prototype 

This board contains the very custom Zilog clock driver chip required to produce a clean 4 MHz square wave with sufficient amplitude.  Only produced for the 4 MHz Z80 CPU prototypes."

The engineer recounted the glory days of the 8-bit CPU wars. "It was a time of excitement and revolution!" "Sharing with the like minded makes it exciting!"

In a follow-up email the engineer who lives on a small island off Washington State wrote a heartfelt remeberance about his former colleage who built the board.

Thank you very much for the interest in the historical roots of the Zilog board. Your expertise in this area is most satisfying!

When Zilog introduced the 4 MHz Z80A, there were several issues that arose. The first problem was the clock input requirements. The solution was to build a little two transistor driver hybrid IC which is the little blue sip on the lower left.

The 16 MHz oscillator gets divided by four by a TTL device (the 9316) and then presented to the CPU via the clock driver. That proved very useful for reliability.

The cpu socket was used in conjunction with an in-circuit emulator for code development and the resulting code is buried in the the 2716 eprom.

The board was actually built by a colleague who worked on support hardware and software while at Zilog. He died a few years ago, so this was part of his work product that he passed along to me prior to his passing.

He was a dear friend and his work helped shape the future of microprocessor based systems.