Happy 50th Birthday to the Zilog z80 CPU

March 1976 - 50 years ago - Mostek delivered the first working samples of the z80 CPU to Zilog. At this point, without their own fabrication plants, Zilog had licensed the chip to Mostek and Synertek for this initial historic production run. Federico Faggin and Masatoshi Shima, former employees of industry giants Intel, had designed the z80 as an inexpensive but powerful alternative to Intel's 8080 CPU.

But this is Sonicstate! So what of the z80's musical legacy? Well, as a general purpose chip, the z80's role in audio isn't obvious like Bobn Yanne's 8-bit glamour duo: SID & DOC. However, look through musical history and you'll see the z80 in a range of significant supporting roles:

• As the main CPU in home computers like the ZX Spectrum and MSX range, the z80 was occasionally called on to playback crude PCM samples by outputting a series of clicks directly to the audio hardware. Furthermore, the z80 was often tasked with music sequencing; drum pattern playback on the SpecDrum, duophonic sample sequences on the RAM Music Machine and, in the case of Yamaha's CX5m MSX Computer: Full-blown MIDI Sequencing, Managing internal FM sound generator voicings and even featuring perhaps the first widely available DX7 voice editor!

• Sega used the z80 as a co-processor in the Mega Drive/Genesis games console and a bunch of arcade motherboards too. Whilst not an audio-playback device, the z80 (given a few KB of it's own dedicated RAM) took the load off the main 68000 CPU(s) by handling assignment of audio; feeding voice data to FM and sample channels.

Finally, the z80 can be found in an array of vintage synthesizers! Here are a few examples:

• Roland Jupiter 8: Patch memory management, Voice Assignment.
• Sequential Prophet 5: As above, but also VCO tuning management & control panel scanning.
• Sequential Prophet 600: Runs the z80 ragged! As above, but also MIDI (note on/off), envelope & LFO generation (via 14-bit DACs - no hardware envelopes) - this lead to some aliasing/zipper noise at some settings; something which Gligli's Teensy upgrade aimed to resolve.

So next time you load up a preset on your Prophet, think of the humble z80 - the little chip that could.

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