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The Z80 and its derivatives and clones make up one of the most commonly used CPU families of all time, and, along with the MOS Technology 6502 family, dominated the 8-bit microcomputer market from the late 1970s to the mid-1980s. Although Zilog made early attempts with advanced mini-computer like versions of the Z80-architecture (Z800 and Z280), these chips never caught on. The company was also trying hard in the workstation market with its Z8000 and 32-bit Z80000 (both unrelated to Z80). In recent decades Zilog has refocused on the ever-growing market for embedded systems (for which the original Z80 and the Z180 were designed) and the most recent Z80-compatible microcontroller family, the fully pipelined 24-bit eZ80 with a linear 16 MB address range, has been successfully introduced alongside the simpler Z180 and Z80 products. Zilog licensed the Z80 core to any company wishing to make the device royalty free, though many East European and Russian manufacturers made unlicensed copies. This enabled a small company's product to gain acceptance in the world market since second sources from far larger companies such as Toshiba started to manufacture the device. Consequently Zilog has made less than 50% of the Z80s since its conception.
Brief history and overviewThe Z80 came about when Federico Faggin, after working on the 8080, left Intel at the end of 1974 to found Zilog with Ralph Ungermann, and by July 1976 they 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 many real improvements over the 8080: An enhanced instruction set including bit manipulation, block move, block I/O, and byte search instructions; New IX and IY index registers and instructions for them; A vectorized interrupt mode (mode 2), as well as a useful "no hardware"-mode (mode 1); Two separate register files, which could be quickly switched, to speed up response to interrupts; A built-in DRAM refresh address mechanism that would otherwise have to be provided by external circuitry; Single 5 Volt power supply; Fewer support chips required for clock generation and interface to memory and I/O; A much lower price; The Z80 quickly took over from the 8080 in the market, and became one of the most popular 8-bit CPUs. Perhaps a key to the success of the Z80 was the built-in DRAM refresh, which allowed systems to be built with fewer support chips. A CMOS version was also developed and the specified maximum clock frequency increased successively from 2.5 MHz up to 8 MHz for the original NMOS design, and up to 20 MHz for the CMOS version sold today, while immediate derivatives such as the Z180 and eZ80 today are specified for 33 and 50 MHz respectively.
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