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. The Z-80 is fully software compatible with the popular 8080A CPU offered from several
sources. Exting designs can be easily converted to include the Z-80 as a superior alternative.
- 2. The Z-80 component set is superior in both software and hardware capabilities
to eny other microcomputer system on the market. There capabilities provide the user
with significantly lower hardware and software development costs while also allowing
him to offer additional features in his system.
- 3. For incresed throughput the Z80 CPU can operate up to a 16 MHz clock rate, offers
the user significant speed advantages over competitive products.
- 4. A complete product line including full software support with strong emphasis
on high level languages and a disk-based development system with real-time debug
capabilities is offered to enable the user to easily develob new products.
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.
OTHER DEVICE NUMBERS
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
Copyright (c) 1995 Zilog, Inc.