The Zilog Z80 has turned 50

The Zilog Z80 has turned 50

Introduction

As of writing, the Zilog Z80 processor was officially launched 50 years ago, in July of 1976, less than 4 years after the last human had walked on the moon, decades closer to WWII than to the present day, roughly at a half way point between the Kennedy assassination and the fall of the Berlin wall, closer to the Korean war than to 9/11 which is itself an event that happened a quarter of a century ago. (Sorry…)

The processor was extremely successful, being used in many 8 bit microcomputers, including early personal computers, home & hobby computers, as well as many embedded, industrial applications.

Together with the 8080 & 8085 that it is binary compatible with, it contributed to creating a de facto hardware standard for 8 bit micros, allowing a de facto software standard of CP/M, and Microsoft BASIC.

The Z80 itself also spawned many clones and derived architectures over the years, famously including the Sharp LR35902, used in the original GameBoy. Zilog themselves eventually gave up their line of 16 and 32 bit derived architectures and returned to Z80 based microcontrollers and variants like the pipelined and higher clocked eZ80, mainly for continued use in industrial applications.

I myself am much too young to have seen the home computing side of this (ignoring the aforementioned GameBoy), but the widespread use in industrial applications means that the original Z80 is still around and in use with Zilog finally discontinuing it mere 2 years ago.

My own first encounter with the Z80 was as a late teenager, when I was browsing an electronics company catalog, surprised to find them still being sold. I designed my own little Z80 computer and convinced a school teacher to let me use the photo lab at night, so I could etch some PCBs.

As several of my former teachers got curious what I was up to, I ended up hearing a lot of interesting anecdotes about old home computers, consoles and a story about DIY wire wrap computer in a Tupperware box, running CP/M and WordStar, hooked up to a "borrowed" IBM terminal that was used to write a thesis on. Over time I ended up being gifted a number of old chips from dusty drawers that made it into my own DIY project, including a bunch of MCS-85 parts, several Z80s, 8085s, 6502s and 6522s.

The whole thing sure taught me a number of interesting lessons about systems engineering and some unexpected ones (reliable power-on reset is surprisingly hard; writing a linker is a lot harder than writing an assembler, writing a compiler is something you can actually do).

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