ZILOG Z80

The Zilog Z80 is an 8-bit microprocessor designed and manufactured by Zilog from 1976 onwards. It was widely used both in desktop and embedded computer designs, and is one of the most popular CPU's of all time. Although Zilog made several attempts to move off the Z80 onto more powerful 16-bit (Zilog Z800) and 32-bit (Zilog Z8000) platforms but other companies were offering CPUs in this performance range years earlier and they never caught on. Today the Z80 remains Zilog's only CPU design in production.

History

The Z80 came about when Federico Faggin left Intel after working on the 8080, and by July 1976 Zilog had the Z80 on the market. It was designed to be binary compatible with the Intel 8080 so that most 8080 code could run unmodified on it, notably the CP/M operating system.

The Z80 offered five real improvements over the 8080:

• a built-in memory controller for DRAM that would otherwise have to be provided by external circuitry
• an enhanced instruction set including new IX and IY index registers and instructions for them
• two instances of each register which could be quickly switched between, to speed up response to interrupts
• a limited ability for SIMD (Single Instruction, Multiple Data) with block move and copy instructions. (These were considered very powerful at the time: modern 3DNow and SSE instructions work on highly advanced versions of the same basic principle.)
• a much lower price

The Z80 quickly took over from the 8080 in the market, and became the most popular 8-bit CPU of all time - indeed, if one takes the absolute size of the market into account, the most successful CPU ever. Later versions increased in speed from the early models' 1 MHz up to as much as 12 Mhz.

Perhaps key to the success of the Z80 was the built-in DRAM controller, which allowed systems to be built with less support chips. Competitor MOS Technologies, maker of the famous 6502 processor, later included this very useful feature in its second generation color video chip VIC-II.

Notable Uses

By the early 1980s it was used in a host of home computer designs including the Radio-Shack TRS-80, Sinclair ZX80¹ & ZX81¹ and ZX Spectrum. It also featured in the great number of fairly anonymous business-oriented CP/M machines (the Osborne 1 being a non-anonymous example) that dominated the market of the time in the way that Windows-based machines do today. In the mid-1980s the Z80 was used in Tatung's Einstein and the Amstrad CPC and PCW home/office computer ranges, as well as the dual-CPU Commodore 128 (to make it CP/M compatible).

Notable later-day uses of the processor include some Texas Instruments (TI) graphing calculators (like the TI-85 and the very popular TI-83), the SNK Neo-Geo video game console (as audio coprocessor), and SEGA Game Gear handheld console with TV. Nintendo's Game Boy and Game Boy Color handheld game systems used a Z80 clone made by Sharp Electronics, which had a slightly different instruction set. The Zilog Z80 has also become a popular embedded microprocessor and microcontroller core, where it remains in widespread use today.

See also: List of home computers by category

Notes

1. The Sinclair ZX80 and -81 were equipped with the Z80 clone NEC 780C

External links

• http://www.z80.info/