Zilog Z80 CPU

The Zilog Z80 is an 8-bit microprocessor designed and manufactured by Zilog. One of the peculiarities of this processor is the coupling of some 8-bit registers to a 16-bit register. This with a 16-bit address bus allows for much faster processing of data than with a conventional 8-bit processor.

This processor was marketed for the first time in July 1976. In the early 1980s it was very popular in the design of 8-bit computers such as Radio Shack TRS-80, Sinclair ZX80, ZX81, ZX Spectrum, MSX standard, Amstrad CPC, PC-88 and later in embedded systems. With the MOS 6502 family, it dominated the 8-bit micro computer market from the late 1970s to the mid-1980s and was still used in then new Amstrad computers until 1995.

The Z80 was designed to be compatible with the Intel 8080, so the majority of the code for 8080 could work without much modification on the Z80. The CP/M operating system was designed around Intel 8080 based systems and could also work without modification on Z80 based systems.Z80 based systems were generally more powerful and had more features than systems based on 8080 CPUs. Some versions of CP/M applications only existed in a Z80 version.

History and overview

The Z80 came into being when Federico Faggin, after working on the 8080, left Intel at the end of 1974 to found Zilog together with Ralph Ungermann to put the Z80 on the market in July of 1976. It was designed to be binary compatible with the Intel 8080 so that most of the 8080 code, including the CP/M operating system, works without modification on it. The Z80 quickly took over share from the 8080 on the market, and became one of the most popular 8-bit processors. Perhaps one of the keys to Z80's success was the integrated refresh of DRAM, and other features that allowed systems to be built with fewer chips. For the first NMOS generation, the maximum clock rate increased gradually. First at 2.5 MHz, then by the well known 4 MHz (Z80a), up to 6 (Z80b) and 8 MHz (Z80h). A CMOS version was developed with frequency limits ranging from 4 MHz to 20 MHz and some versions were sold until the 2000s. The CMOS version also has a low power sleep mode, with processor state retention. The Z180 and eZ80, fully compatible derivatives, have specifications for up to  50 MHz.

Use in systems

The Z80 CPU saw uses including in Texas Instruments calculators, SEGA Master System, GameBoy, and Game Gear video game consoles. Some more powerful consoles with other central processors like the Neo Geo or the Mega Drive with its Motorola 68000, used the Z80 as an addon processor to handle sound or system I/O.