Zilog Z80 turns 50 as an open-source replacement heads to drop-in DIP40 silicon — iconic 8-bit CPU launched in July 1976 and was discontinued in 2024

The Z80 CPU is nearing its End of Life, but one developer hopes to resurrect it with a clone. — (Image credit: Mister rf, CC BY-SA 4.0 , via Wikimedia Commons)

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

The original Z80 packed 8,500 transistors on a 4μm process and typically ran at 2.5 MHz, with later CMOS variants reaching 20 MHz. Binary compatibility with the Intel 8080 let it absorb the existing CP/M software base, with an on-die DRAM refresh counter that cut the number of support chips a system needed. Development of working prototypes cost roughly $400,000 against $500,000 in funding from Exxon, per the Computer History Museum.

The chip powered the ZX Spectrum, TRS-80, MSX machines, Nintendo's Game Boy, Sega's Master System, the Pac-Man arcade cabinet, and Texas Instruments' graphing calculators, then shipped in industrial controllers for decades after home computing moved on to more powerful successors. Zilog's end-of-life notice, dated April 15, 2024, told customers its wafer foundry was discontinuing support for the Z84C00 family, and last-time-buy orders closed that June.

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However, Renaldas Zioma's FOSS Z80 project, launched shortly after the end-of-life notice, now has working silicon. The first version, fabbed on SkyWater's 130nm node through Tiny Tapeout 7 on a die of just 0.064mm², has been confirmed as functional via the project’s GitHub repository. A QFN64 version with all 40 pins exposed followed on the Efabless CI2406 shuttle, two further runs then went through IHP's 130nm process, and the current run targets the classic DIP40 form factor using chip-on-board assembly on GlobalFoundries' 180nm GF180MCU node via Wafer.Space. The end goal here is to fab a drop-in replacement for machines like the ZX Spectrum and RC2014 kits.

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

Zilog is trimming the Z80's official successor line as well. A product change notification from last October put the eZ80L92, along with several Z8F-series microcontrollers, on end-of-life, citing "little to no demand." Last-time-buy orders closed on January 20 this year, with shipments scheduled through April 20, 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.

Hobbyists keep finding work for the original chip regardless. For example, earlier this year, a developer ran a tiny conversational AI on a Z80 with 64KB of RAM.

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Luke James is a freelance writer and journalist. Although his background is in legal, he has a personal interest in all things tech, especially hardware and microelectronics, and anything regulatory.

14 Comments Comment from the forums

hwertz

Conversational LLM on a 64KB Z80? I bet that was a pretty sweet conversation LOL.

Anyway the Z80 is a classic and it's great it's still available.
Reply
roelh

A Z80 can be replaced by a circuit of 60 TTL IC's, without FPGA. This includes a 640x400 VGA, in color. It runs a nice GUI, and you can build it yourself. Search: Isetta computer. AFAIK it is the first time that the Z80 was replicated by a TTL circuit. The Isetta also runs ZX Spectrum games.
Reply
TheThief

The Gameboy doesn't use a Z80 - it uses a Sharp SM83.

The SM83 lies about halfway between the 8080 and Z80 - it is also compatible with the 8080, has some extended opcodes from the Z80 but not all, doesn't have the index or shadow registers, doesn't have the DRAM refresh, etc. It does however have built in timers, and the variant in the GB has built in display and sound capabilities as well.
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abufrejoval

My first physical encounter with computers was via Z-80 machines. A BASIC programming course in 1980 used Tandy TRS-80 machines and the first computer I owned, an Apple ]

generic, even if the base architecture didn't permit every imaginable permutation... it was a battle of abstraction layers and I always aimed as high as possible there, but demanded (and checked) ultimate effiency from the compiler. And most importantly, I demanded that compilers catch all those stupid errors my fast fat fingers and my sloppy brain introduced while "speaking via the keyboard". There Turbo Pascal was both brutal and fast, Fortran and C compilers were so 'permissive', I might have failed in an IT career, but then I caught them producing assembly garbage, too.

Perhaps because of that culture war, I stayed clear of writing any significant amount of assymbly code, then or ever after. But I certainly read the CP/M (Intel) assembly source code, just I read the C-source of Unix years later. I also read the assembly code that compilers produced for many years to gauge their quality (or lack thereof).

As with human languages, understanding and speaking are two very distinct beasts: I clearly understand just about every Romance language ever invented much better than the Germanic variants that surround my native German, it doesn't mean I'd be ready to write contracts in each, I'd be confortable to sign: with code you not only expect it to work, but also to manage every imagined borderline condition.

So in a way the Z-80 has in all likelyhood been much more of a formative experience, even if all of my (paid) IT career has been x86 and rarely below K&R or even ANSI C when writing code.

Z-80 (when did it ever drop the dash?), I salute you, Federico & Masatoshi, you've done great work, thank you very much!
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pjmelect

The good thing was that most Z80's could be overclocked from 2.5 MHz to more than 8MHz providing the memory of the computer was fast enough. try overclocking by the same percentage modern CPU's
Reply
abufrejoval

pjmelect said:
The good thing was that most Z80's could be overclocked from 2.5 MHz to more than 8MHz providing the memory of the computer was fast enough. try overclocking by the same percentage modern CPU's
That wasn't an option with the SoftCard on the Apple ]

Reply
80251

I believe the Z80 was pin compatible and instruction set compatible w/Intel's 8088 and could almost be used interchangeably w/the 8088. It broke any programs that relied on timing loops being executed according to the speed of 8088 instructions though and some games would run so much faster on the Z80 as to be unplayable.
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ttquantia

80251 said:
I believe the Z80 was pin compatible and instruction set compatible w/Intel's 8088 and could almost be used interchangeably w/the 8088.
No. 8088 has the same instruction set as 8086.
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80251

ttquantia said:
No. 8088 has the same instruction set as 8086.
All three CPUs were based on the Intel 8080 because the founder of Zilog formerly worked at Intel on the 8080!
Reply
ttquantia

80251 said:
All three CPUs were based on the Intel 8080 because the founder of Zilog formerly worked at Intel on the 8080!
Maybe, but 8086 (followed by the 8-bit variant 8088) started the so-called x86 instruction set, which you may have heard about. It is a different instruction set than Z80 and 8080.
Please check before posting disinformation.
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