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The Zilog Z80 is an 8-bit microprocessor designed and manufactured〔Early chips were manufactured by Mostek and Synertek, before Zilog had its own manufacturing factory ready, in 1977. These companies were chosen because they could do ion implantation. This was needed for the depletion-mode MOSFETs that the Z80 design used as load transistors in order to cope with a single 5 Volt power supply. (Today, however, Zilog is a "fabless" company again.)〕 by Zilog. It was launched in July 1976 and was widely used in both desktop computers and embedded systems, including military applications. The Z80 and its derivatives were one of the most commonly used CPUs of all time, and, along with the MOS Technology 6502 family, dominated the eight-bit microcomputer market from the late 1970s to the mid-1980s.〔 Zilog licensed the Z80 design to several vendors, though many East European (for instance, 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. 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. == History == The Z80 came about when Federico Faggin left Intel at the end of 1974 to found Zilog with Ralph Ungermann. Until he left, Faggin had been working on the Intel 8080 and by July 1976, their new Zilog had developed the Z80 and launched it onto the market. Faggin designed the instruction set to be binary compatible with the Intel 8080 so that most 8080 code, notably the CP/M operating system and Intel's PL/M compiler for 8080 (as well as its generated code), would run unmodified on the new Z80 CPU. Masatoshi Shima, the principal logic and transistor level-designer of the 4004 and the 8080, under Faggin's supervision at Intel, also designed most of the microarchitecture as well as the gate and transistor levels of the Z80 CPU at Zilog, assisted by a small number of engineers and layout people. The Z80 offered many improvements over the 8080:〔 * An enhanced instruction set including bit manipulation, block move, block input/output (I/O), and byte search instructions * New IX and IY index registers with instructions for direct ''base+offset'' addressing * A better interrupt system * * A more automatic and general vectorized interrupt system, ''mode 2'', primarily intended for Zilog's line of counter/timers, DMA and communications controllers, as well as a fixed vector interrupt system, ''mode 1'', for simple systems with minimal hardware (with ''mode 0'' being the 8080-compatible mode). * * A non maskable interrupt (NMI) which can be used to respond to power down situations and/or other high priority events (and allowing a minimalistic Z80 system to easily implement a two-level interrupt scheme in ''mode 1''). * * Two separate register files, which could be quickly switched, to speed up response to interrupts or provide extra register space for applications. * Less hardware required for power supply, clock generation and interface to memory and I/O * * Single 5 volt power supply (''the 8080 needed -5 V/+5 V/+12 V''). * * Single-phase 5 V clock (''the 8080 needed a high-amplitude (9 to 12 volt) non-overlapping two-phase clock''). * * A built-in DRAM refresh mechanism that would otherwise have to be provided by external circuitry (although this necessarily reduced the i-fetch access from 3 cycles to 2 cycles, and, therefore, required substantially faster EPROMs than the 8086/8088). * * Non-multiplexed buses (''the 8080 had state-signals multiplexed onto the data bus''). * A special reset function which clears only the program counter so that a single Z80 CPU could be used in a development system such as an in-circuit emulator. The Z80 took over from the 8080 and its offspring, the 8085, in the processor market,〔(【引用サイトリンク】 Z80, the 8-bit Number Cruncher )〕 and became one of the most popular 8-bit CPUs.〔〔 Perhaps a key to the initial success of the Z80 was the built-in DRAM refresh, and other features which allowed systems to be built with fewer support chips (Z80 embedded systems typically use static RAM and hence do not need this refresh). For the original NMOS design, the specified upper clock frequency limit increased successively from the introductory 2.5 MHz, via the well known 4 MHz (Z80A), up to 6 (Z80B) and 8 MHz (Z80H). A CMOS version was also developed with specified frequency limits ranging from 4 MHz up to 20 MHz for the version sold today. The CMOS version also allowed a low-power sleep with internal state retained (having no ''lower'' frequency limit). The fully compatible derivatives HD64180/Z180 and eZ80 are currently specified for up to 33 and 50 MHz respectively. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Zilog Z80」の詳細全文を読む スポンサード リンク
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