Zilog Z80

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Z80 CPU from the very beginning in a white ceramic case
Zilog Z80 in 40-pin DIP

The Zilog Z80 is an 8-bit microprocessor developed by Zilog Inc. The Z80 is still available today in CMOS technology.

He was born shortly after Federico Faggin , the company Intel to leave and his own company founded Zilog. At Intel he worked on the 8080 microprocessor.

The Z80 was launched in March 1976. It was developed under the condition of being binary downward compatible with the Intel 8080. Thus, the most developed for the 8080 programs without modification was geared in particular the CP / M - operating system .

Differences to the 8080

Architecture of the Z80

The Z80 has several advantages over the Intel 8080 : A single 5 V supply voltage instead of +5 V / −5 V / + 12 V with the 8080, a built-in refresh control for DRAM , which otherwise had to be implemented externally, sophisticated interrupt Functions , block copy and compare commands, block IO operations and 16-bit registers (IX and IY) with indexed addressing, further 16-bit arithmetic commands (ADC, SBC), further bit and shift commands, faster execution times (simple commands last 4 instead of 5 bars), a double set of registers and a lower price.

In addition, the mnemonics of the assembly language have been simplified: While the commands for data transport on the 8080, for example, still differentiate between internal and external loading processes, the Z80 only has the LD command. However, this is not a change in the technology of the processor itself, just a matter of convention; the assemblers for the Z80 generate the same machine code from the new instructions as the 8080 assembler from the old instructions.


Op-Code   8080-Mnemonik  Z80-Mnemonik  Funktion
79        MOV A,C        LD A,C        kopiert den Inhalt des Registers C in das Register A
02        STAX B         LD (BC),A     kopiert den Inhalt des Registers A in die Adresse, die im Registerpaar BC steht
3A 34 12  LDA 1234h      LD A,(1234h)  kopiert den Inhalt der Adresse 1234h in das Register A


The Z80 quickly surpassed the 8080 and became the most widely used 8-bit CPU to date . If you include the absolute size of the market, it is the most successful CPU since then.

Initially, the Z80 was manufactured by Mostek for Zilog until Zilog had built its own factories. Therefore, Mostek also had a license to market the Z80 under the name MK3880. The Z80 was later also manufactured under license by other semiconductor manufacturers such as NEC . Later versions allowed a higher clock rate than the original 2.5  MHz , the Z80A offered 4 MHz, the Z80B 6 MHz and the Z80H then 8 MHz. In addition, the energy-saving Z80L (L for LowPower) as well as variants in CMOS technology, which could then even be operated up to 20 MHz, were created.

Other interesting properties of this CPU are additional commands that have not been documented by the manufacturer. In particular, the prefix opcodes for the IX and IY registers can be applied to practically all commands that otherwise affect the HL register pair or only the H or L registers. It is thus possible to use only the upper or lower half of IX or IY as an 8-bit register.

In addition to the classic Intel peripheral modules, a number of Zilog peripheral modules are available for the construction of microcomputers, which were specially developed for the Z80 and can work with the effective interrupt vectors. The most important of the Z80 family are PIO (parallel input / output), SIO (serial input / output), CTC (counter and timer) and DMA (direct memory access by peripheral devices). This was followed later by space-saving, more highly integrated components which, in addition to serial and parallel interfaces, also offered counters / timers and interrupt controllers on one chip, such as B. KIO, multifunctional as they are still standard in today's single-chip MCUs.


Z80 processor from the 2000s in QFP form

Initially, the Z80 was widely used in arcade games , such as Galaxian (1979) and Pac-Man . The Z80 proved itself as a game processor until the end of the 1980s. In order to achieve the desired effects, machine manufacturers later also used up to three Z80s in parallel. In the 1986 arcade game Noboranka , numerous sprites and animations were made possible by the 20 MHz version of a Z80. The shoot 'em up Zaxxon from 1982, for which a 3 MHz Z80 CPU was used, clearly showed the potential of the Z80. Also Mr. Do! , which appeared in 1982, two years after Pac-Man, already shone with physical effects, using a 4.1 MHz Z80.

Until 2004, the Neo-Geo machines used it as a sound processor. E-mu Systems already used it in its synthesizers in the year of publication after tests with an Intel 8080 had failed. In the late 1970s and early 1980s the Z80 was used in many newly developed home computers , for example the Tandy TRS-80 , Nascom , Video Genie , Color Genie , PC-8801 ; in the MZ-80 and MZ-700 and 800 series from Sharp; in the Triumph Adler Alphatronic PC ; in the Schneider / Amstrad CPC ; the Amstrad PCW = Schneider "Joyce", with the Sinclair ZX80 , ZX81 and ZX Spectrum , the Commodore C128 (as a second processor), in MSX computers and a large number of rather unknown business-oriented CP / M machines that dominated the market at that time like the Windows PCs today. The main competitor of the Z80 in the home computer sector was the MOS Technologies 6502 , the variants of which could be found in the Apple II , Commodore 64 and 8-bit Ataris .

Many Apple II computers were equipped with an expansion card with a Z80 processor in order to be able to use CP / M. Since these Z80 cards were copied in large quantities and operated with unlicensed CP / M copies, no precise figures are available about their distribution. However, this combination is likely to be one of the most common CP / M systems. The Basis 108 , a hybrid computer and extensive replica of the Apple II architecture, also contained a Z80 in addition to the typical Apple 6502 and was able to use programs under the CP / M operating system in addition to Apple software, such as the WordStar word processor, which was popular at the time .

Later the processor was also used in Texas Instruments pocket calculators (even today in the TI-83 Plus , TI-84 Plus and TI-84 Plus Silver Edition ), in SNK's Neo Geo as a sound co-processor and Sega's game consoles Master System and Game Gear Uses; the Sega Mega Drive used it as a coprocessor for audio output. Nintendo's game consoles Game Boy and Game Boy Color used a Z80 clone (DMG CPU) manufactured by Sharp . It has a slightly modified set of instructions.

The Z80 also became popular with embedded systems and is still widely used there today, for example in Toshiba's microcontroller families TLCS-90 and TLCS-870 a Z80 core works in a wide variety of combinations of memory and peripheral equipment. The Z80 is also used for the digital control of the analogue sound generator hardware in the Tiracon 6V hybrid synthesizer , which was manufactured in the GDR by VEB AAC Cottbus from 1986 to 1989 . However, neither the clones of the Z80 manufactured in the Soviet Union nor the GDR clones of the Z80 were used (see versions).

After the advent of more powerful 16-bit CPUs, the large amount of existing 8-bit software (mainly under CP / M ) was kept usable with the help of software emulators .

Even today (2012), the Z80 is often used as a model of a CPU at many universities alongside other 8-bit CPUs such as the 8080 or the 6502. At the Vienna University of Technology it is presented in the subject "Digital Systems" as MC8 (Modellcomputer-8), whereby the instruction set has been simplified, own assembler mnemonics have been defined and certain registers, addressing types and special functions of the CPU are not used to reduce the learning effort to lower.


First series of the U880 CPU from the Funkwerk Erfurt
The semiconductor technology of a U880 (MME 80A-CPU, MME9201)
T34BM1 in a white ceramic case from the Soviet Union
NEC µPD780C, NEC version of a Z80
NMOS series
  • "Z80 CPU" (first series had no number, 2.5 MHz)
  • Z8400 ("Z80 CPU", 2.5 MHz)
  • Z8400A ("Z80A CPU", 4 MHz)
  • Z8400B ("Z80B CPU", 6 MHz)
  • Z8400H ("Z80H CPU", 8 MHz)
  • Z0840004 (4 MHz)
  • Z0840006 (6 MHz)
  • Z0840008 (8 MHz)
CMOS series
  • Z84C0004 (4 MHz)
  • Z84C0006 (6 MHz)
  • Z84C0008 (8 MHz)
  • Z84C0010 (10 MHz)
  • Z84C0020 (20 MHz)
  • Z84C00-4PS (4 MHz)

In the GDR , a non-licensed replica of the Z80 was developed under the name U880 due to a trade embargo .

There it was the dominant processor in a countless number of commercial computers (PC-1715, A-5120, MC-80), educational computers (KC 85-1 / 87, KC-85 / 2-4, BIC A-5105, LC -80), do-it-yourself computers (Z-1013) up to replicas of Z80-based computers (ZX81, ZX Spectrum). Clock frequencies were between 1 MHz and just under 4 MHz. In the Soviet Union, unlicensed replicas under the names T34BM1 and KR1858BM1 ( Russian Т34ВМ1 and КР1858ВМ1 ) were produced by various factories (including "Elektronika", "Integral", "Angstrem", "Transistor") well into the 1990s. Replicas with data codes from 1996 are known.

Successor types:

  • Z180 : From 1985 Hitachi introduced a microcontroller under the name HD64180, which was particularly successful because of the integration of numerous peripheral components. Later, Zilog also manufactured the chip as the Z180.
  • Toshiba combined the Z80 processor with its peripheral components CTC, SIO and PIO, together with an oscillator and watchdog function in a 100-pin housing as the TMPZ84C015. The component is still produced today, with Zilog as the second manufacturer, designation Z84C15.

From Zilog followed:

  • Zilog Z84C01 Z80 code compatible CPU, but different pin assignment, internal clock generator and control of the HALT behavior
  • Z280 16 bit + MMU (16  MiB address space) + 256 byte cache
  • Z380 16 bit with 32 bit registers (up to 4 GiB address space) and four pipelines

Currently sold:

Other, non-Z80-compatible CPU types from Zilog:


Both books are still considered standard works in the field of microprocessors today.

  • Ramesh Gaonkar: The Z80 Microprocessor: Architecture, Interfacing, Programming, and Design. Macmillan Publ. Co. New York 1988, ISBN 0-675-20540-9 .
  • Eberhard Zehendner: The Z80 book. Markt & Technik, ISBN 3-89090-219-7 .

Web links

Commons : Zilog Z80  - collection of images, videos and audio files

Individual evidence

  1. Bernd Leitenberger: Intel's defeat: The Z80 bernd-leitenberger.de, accessed on May 15, 2019.
  2. ... about CP / M Computermuseum Munich, accessed on May 15, 2019.
  3. Homepage. In: mamedev.org, accessed on November 15, 2018 (information screens in the MAME emulator at startup).
  4. Rob Keeble: 30 Years of Emu. (No longer available online.) In: soundonsound.com. September 2002, archived from the original on March 14, 2012 ; accessed on November 15, 2018 .