Zilog Z80 Turns 50 as Open-Source Drop-In Replacement Nears Production

The Zilog Z80, the iconic 8-bit processor that first went on sale in July 1976, has just turned 50 years old. The chip remained in production for 48 years until Zilog — now a Littelfuse subsidiary — stopped accepting orders in June 2024. However, a community-funded, open-source replacement is now closer than ever to shipping in the chip's original 40-pin DIP package.

Original Specifications and History

• Transistor count: 8,500 on a 4μm process
• Typical clock speed: 2.5 MHz (later CMOS variants reached 20 MHz)
• Key feature: Binary compatibility with the Intel 8080, allowing it to absorb the existing CP/M software base
• On-die DRAM refresh counter reduced the number of support chips required
• Development cost: Roughly $400,000 against $500,000 in funding from Exxon, per the Computer History Museum

Notable Systems Powered by the Z80

• ZX Spectrum
• TRS-80
• MSX machines
• Nintendo's Game Boy
• Sega's Master System
• Pac-Man arcade cabinet
• Texas Instruments' graphing calculators

The chip also shipped in industrial controllers for decades after home computing moved on to more powerful successors.

End of Production

Zilog's end-of-life notice, dated April 15, 2024, informed customers that its wafer foundry was discontinuing support for the Z84C00 family. Last-time-buy orders closed in June 2024.

Open-Source Replacement Progress

Renaldas Zioma's FOSS Z80 project, launched shortly after the end-of-life notice, now has working silicon:

• First version: Fabbed on SkyWater's 130nm node through Tiny Tapeout 7 on a die of just 0.064mm² — confirmed functional via the project's GitHub repository
• QFN64 version: All 40 pins exposed, fabricated on the Efabless CI2406 shuttle
• Two further runs: Processed through IHP's 130nm process
• Current run: Targets the classic DIP40 form factor using chip-on-board assembly on GlobalFoundries' 180nm GF180MCU node via Wafer.Space

The end goal is to produce a drop-in replacement for machines like the ZX Spectrum and RC2014 kits.

Performance and Design

The design is built around Guy Hutchison's TV80 Verilog core. The project's Tiny Tapeout page states that the 130nm CMOS implementation should support clocks up to 50 MHz, compared to 4 MHz for the original NMOS part.

Official Successor Line Trimming

Zilog is also winding down the Z80's official successor line:

• A product change notification from October 2024 placed the eZ80L92 and several Z8F-series microcontrollers on end-of-life, citing "little to no demand"
• Last-time-buy orders closed on January 20, 2025, with shipments scheduled through April 20, 2025, on non-cancelable, non-returnable terms
• The eZ80L92 is the only eZ80 part named in the notice
• The pipelined eZ80 architecture, introduced in 2001 and still inside TI's current TI-84 Plus CE calculators, otherwise remains in Zilog's catalog

Ongoing Hobbyist Use

Hobbyists continue to find work for the original chip. Earlier this year, a developer ran a tiny conversational AI on a Z80 with 64KB of RAM.

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