Zilog Z80 CPU – Modern, free and open source silicon clone


On April 15 of 2024 Zilog has announced End-of-Life for Z80, one of the most famous 8-bit CPUs of all time.

It is a time for open-source and hardware preservation community to step in with a Free and Open Source Silicon (FOSS) replacement for Zilog Z80.

The first fabrication of FOSS Z80 is scheduled for June of 2024!

Zilog Z80 modern free and open source silicon clone

On the path to become a silicon proven, pin compatible, open-source replacement for classic Zilog Z80.

FOSS Z80 leverages OpenROAD flow and FOSS 130 nm Skywater PDK to synthesize production ready silicon. Tiny Tapeout infrastructure is used to test and pool design with many others to reduce the cost of physical chip fabrication at Skywater Foundries.

The first iteration of FOSS Z80 silicon

The first iteration is developed with Tiny Tapeout 07 using 130 nm process and fits on a 0.064 mm2 die area. The first fabrication is scheduled for June of 2024 as a part of CI 2406 Shuttle.

The implementation is based around Guy Hutchison’s TV80 Verilog core.

Read documentation for Tiny Tapeout 07 version

Below is the image of GDSII integrated circuit layout for FOSS Z80. It is the result of automatic place-and-route flow in OpenROAD using 130 nm “gates” logic elements.

Further Plan / ToDo

  • Add thorough instruction (including ‘illegal’) execution tests ZEXALL to testbench
  • Compare different implementations: Verilog core A-Z80, Netlist based Z80Explorer
  • Tapeout with ChipIgnite in QFN44 package
  • Tapeout with DIP40 package
  • Create gate-level layouts that would resemble the original Z80 layout, see the original chip dies below. Zilog designed Z80 by manually placing each transistor by hand.




Oral History of the Development of the Z80

Oral History Panel on the Founding of the Company and the Development of the Z80 Microprocessor

M. Shima on Demystifying Microprocessor Design

Z80 Patents

  • (expired) Patent US4605980 — input voltage spike protection
  • (expired) Patent US4332008A — ???
  • (expired) Patent US4486827A — reset circuitry

Z80 Die shots

Z80 Reverse Engineering

Existing Z80 implementations

What is Tiny Tapeout?

Tiny Tapeout is an educational project that aims to make it easier and cheaper than ever to get your digital designs manufactured on a real chip.

To learn more and get started, visit


Related Articles

Back to top button