#01 Zilog Z80 Processor: Architecture, History and Computers
1. Processor Architecture and Design The Zilog Z80 is an 8-bit microprocessor with a 16-bit address bus, designed using CISC (Complex Instruction Set Computer) architecture. The chip was built using NMOS technology with 8500 transistors and requires a single +5V power supply. 1.1 Internal Organization The Z80 contains 208 bits of R/W memory available to the programmer, organized into eighteen 8-bit registers and four 16-bit registers. All registers are implemented using static RAM. General-purpose registers: 16-bit special registers: 1.2 ALU Unit The Arithmetic Logic Unit (ALU) is 4-bit despite the processor’s 8-bit architecture. It performs the following operations: 1.3 Instruction Set The Z80 offers 158 instructions ranging from one to four bytes in length. 252 instructions are single-byte for increased performance, with the remainder being 2, 3, or 4-byte instructions. The processor is fully compatible with Intel 8080 but offers a significantly extended instruction set. 2. Development History 2.1 Founding of Zilog The history of Z80 began in 1974 when Federico Faggin left Intel following disagreements about the company’s development direction. Faggin, the chief architect of Intel 4004 and 8080 processors, met with Ralph Ungerman and proposed founding their own microprocessor company. Federico Faggin / www.frontiere.polimi.it “I asked Ralph if he wanted to go for a drink and said: ‘Ralph, I’d like to start a microprocessor company, are you interested?’ And he replied: ‘Yes! Let’s do it!’ And that was it. There was no discussion about what we would do, how we would do it, and so on” Zilog was founded in California in 1974 with financial backing from Exxon. The name derives from “Z integrated logic”, where “Z” was meant to signify “the last word in integrated logic”. 2.2 Design Team Masatoshi Shima joined the team in 1975 – the chief designer of logic and transistor circuits for Intel 4004 and 8080 processors. Shima was responsible for logic implementation and transistor-level design. The entire venture initially employed only 11 people: 2.3 Design Process Federico Faggin performed a manual design of the entire chip on paper, drawing each of the process masks for all 8500 transistors. The layout took about 15 weeks. Masatoshi Shima then conducted manual verification of the design, using simple measuring instruments to check whether the sizes and spacing between each of the 8500 transistors and all connections met the process technology requirements. This manual process took him several weeks. 3. Evolution and Variants 3.1 Basic Z80 Versions Zilog produced several processor variants with different clock speeds: 3.2 Later Extensions Z180 (1985) – extended version with 16-bit addressing, DMA controllers, and built-in serial ports eZ80 (2001) – modern successor offering: 4. Computers Using Z80 4.1 American Pioneers TRS-80 (1977) – one of the first mass-market microcomputers produced by Radio Shack/Tandy photo: dunfield.classiccmp.org Radio Shack TRS-80 vintage computer with Z80 processor, monitor, and cassette recorder Timex Sinclair 1000 (1982) – American version of ZX-81 with Z80A 3.25 MHz processor, 2 KB RAM, and 8 KB ROM. Dimensions 167 × 175 × 38 mm, weight 350 g. Timex Sinclair 2068 (1983) – enhanced American version of ZX Spectrum with Z80A 3.58 MHz processor, 48 KB RAM, 24 KB ROM, AY-3-8912 sound chip, and cartridge port. Advertised as a “72 KB” computer (48 KB RAM + 24 KB ROM). ColecoVision (1982) – gaming console using Z80 as the main processor 4.2 British Icons ZX Spectrum (1982) – iconic home computer from Sinclair that dominated British and European markets. Produced in various versions throughout the 1980s. photo: https://oldcomputers.net Sinclair ZX Spectrum home computer, an iconic vintage 8-bit machine powered by the Z80 processor Amstrad CPC (1984) – series of Colour Personal Computers offering advanced graphics for their time Camputers Lynx (1983) – lesser-known British home computer 4.3 Japanese standard MSX (1983) – unified computer standard created by ASCII and Microsoft, adopted by many Japanese companies. MSX2 (1985) was an extended version of this standard. 4.4 European Timex Computers Timex Computer 2048 (1985) – European version of TC2068 with Z80A 3.5 MHz processor, 48 KB RAM, 16 KB ROM, 256×192 graphics in 8 colors, and monophonic sound. Produced by Timex’s Portuguese division. Timex Computer 2068 – European variant of American TS2068 with modifications to increase compatibility with original Sinclair. Differed with PAL modulator instead of NTSC and 9V instead of 15V power supply. 4.5 Gaming Consoles Sega Master System (1985) – 8-bit home console using Z80 clocked at 3.58 MHz. Known as Sega Mark III in Japan. Nintendo Game Boy (1989) – portable console using a Z80 clone (GB-Z80) manufactured by Sharp Corporation with modified instruction set. Game Boy Color (1998) also used a similar chip. Sega Game Gear (1990) – portable version of Master System with smaller screen but better color palette. 4.6 Polish Implementations Meritum (1983/1985) – family of computers based on TRS-80 Model I, produced by Mera-Elzab in Zabrze. Used U880D clone from East Germany instead of original Z80. Meritum specifications: Meritum 3 / Author: Joee , CC BY 3.0 Elwro 800 Junior (1986) – educational computer also using U880D clone. More popular in schools than Meritum due to better graphics capabilities. Unipolbrit 2086 (1986) – assembled in Poland by Gdansk-based Unimor in cooperation with Polonia company Polbrit, version of TC-2068. miSTER Z80 – product by ZEG Tychy for laboratory and office applications 4.7 Other European Systems Tatung Einstein – British computer with Z80A 4 MHz, 64 KB RAM, TI TMS9918 graphics chip Elan Enterprise (1985) – Hungarian home computer Sam Coupé (1989) – ZX Spectrum successor with enhanced capabilities Sam Coupe / Simon Owen, CC BY-SA 3.0 4.8 Arcade Applications Z80 found wide application in arcade games: Classic games like Pac-Man used Z80 as main processor In later systems, Z80 served as audio coprocessor (e.g., Neo Geo, Sega Mega Drive) 4.9 Modern Implementations Spectrum NEXT (2020) – modern reimplementation of ZX Spectrum maintaining Z80 compatibility Spectrum NEXT / https://www.specnext.com Various FPGA implementations allow running Z80 in programmable logic devices, enabling modernization of old systems. 5. DIY Computers and Hobby Projects 5.1 RC2014 – Modular Z80 System RC2014
