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Z80 CPU Introduction

  • The term "microcomputer" has been used to describe virtually every type of small computing device designed within the last few years. This term has been applied to everything from simple "microprogrammed" controllers constructed out of TTL MSI up to low end minicomputers with a portion of the CPU core constructed out of TTL LSI "bit slices". However, the major impact of the LSI technology within the last few years has been with MOS LSI. With this technology , it is possible to fabricate complete and very powerful computer systems with only a few MOS LSI components.

  • The Zilog Z-80 family of components is a significant advancement in the state-of-the-art of microcomputers. These components can be configured with any type of standard semiconductor memory to generate computer systems with an extremely wide range of capabilities. For axample, as few as two LSI circuits and tree standard TTL MSI pakages can be combined to form a simple controller. With additional memory and I/O devices a computer can be constructed with capabilities that only a minicomputer could previously deliver. This wide range og computational power allows standard modules to be constructed by a user tha can satisfy the requirements of an extremely wide range of applications.

  • The major reason for MOS LSI domination of the microcomputer market is the low cost of these LSI components. For example, MOS LSI micropomputers have already replaced TTL logic in such applications as teminal controllers and test systems. In fact the MOS LSI microcomputers is finding its way into almost every product that now uses electronics and it is even replacing many mechanican systems such as weight scales and automobile controls.

  • The MOS LSI microcomputer market is already well established and new products using them are bing developed at an extraordinary rate. The Zilog Z-80 components set has been designed to fit into this market through the following factors:
    Microcomputer systems are extremely simple to construct using the Z-80 components. Any such system consists of tree parts:
  • 1. Z80 CPU (Centrel Processing Unit)
  • 2. Memory (ROM and RAM)
  • 3. Interface circuits to peripheral devices

    The CPU is the heart of the system. Its function is to obtain instructions from the memory and perform the desired operations. The memory is used to contain instructions and in most cases data that is to be processed. For example, a typical instruction sequence may be to read data from a specific peripheral device, store it in a location in memory, check the parity and write it out to another peripheral device. Note that the Zilog component set includes the CPU and various general purpose I/O device controllers, while a wide range of memory devices may be used from any source. Thus, all required components can be connected together in a very simple manner with virtually no external logic. The user's effort then becomes primarily one of software development. That is, the user can concentrate on describing his problem and translating it into a series of instructions that can bo loaded into a microcomputer memory. Zilog is dedicated to making this step of software generation as simple as possible. A good example of this is our assembly language in which a simple mnemonic is used to represent every instruction that the CPU can perform. This language is self documenting in such way that from the mnemonic the user can understand exactly what the instruction is doing without constantly checking back to a complex cross listing.


    The Z80 microprocessor is an 8 bit CPU with a 16 bit address bus capable of direct access of 64k of memory space. It has a language of 252 root instructions and with the reserved 4 bytes as prefixes, acceses an additional 308 instructions. The Z80 was modeled after the 8080 and contains the 78 - 8080 opcodes as a subset to it's language.

    Programming features include an accumulator and six eight bit registers that can be paired as 3-16 bit registers. In addition to the general registers, a stack-pointer, program-counter, and two index (memory pointers) registers are provided. While not in the same leauge as the 80486 or 68000 series, the Z80 is extremely useful for low cost control applications. One of the more useful features of the Z80 is the built-in refresh circuitry for ease of design with DRAMs.

    The Z80 comes in a 40 pin DIP package. And resently also in a 44 pin SMD and QFP. It has been manufactured in A, B, and C models, differing only in maximum clock speed. It also has been manufactured as a stand-alone microcontroler with various configurations of on-chip RAM and EPROM.



    Max. Clock Speed: Z80 - 2.5MHz, Z80A - 4MHz . NEW models up to 25MHz!!
    Power Requirements: Z80 - 5V@60mA, Z80A - 5V@90mA
    Operating Temp: 0 - 70 deg C.
    Min. Instruction time: 1uS (@4MHz)
    Max. Instruction time: 5.75uS (@4MHz)
    No. of Instructions: 158 (78 instructions of 8088 are a subset)
    Internal Registers: 14
    Stack: RAM
    Copyright (c) 1995 Zilog, Inc.