Introduction - ZiLOG Z80-CPU Technical Manual

1.0 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 "microprogram-
med" controllers constructed out of TTL MSI up to low end minicomputers with a portion of the CPU
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 power-
ful 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 micro-
computers. These components can be configured with any type of standard semiconductor memory to
generate computer systems with an extremely wide range of capabilities. For example, as few as two LSI
circuits and three standard TTL MSI packages 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 of computational power allows standard modules to be constructed by a
user that 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 few LSI components. For example, MOS LSI microcomputers have already replaced TTL logic in
such applications as terminal controllers, peripheral device controllers, traffic signal controllers, point of
sale terminals, intelligent terminals and test systems. In fact the MOS LSI microcomputer is finding its way
into almost every product that now uses electronics and it is even replacing many mechanical systems such
as weight scales and automobile controls.
The MOS LSI microcomputer market is already well established and new products using them are
being developed at an extraordinary rate. The Zilog Z-80 component set has been designed to fit into
this market through the following factors:
1. The Z-80 is fully software compatible with the popular 8080A CPU offered from several sources.
Existing 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 any other micro-
computer system on the market. These 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 increased throughput the Z80A operating at a 4 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 advanced real-time debug capabilities is offered to enable
the user to easily develop new products.
Microcomputer systems are extremely simple to construct using Z-80 components. Any such system
consIsts of three parts:
L CPU (Central Processing Unit)
2. Memory
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
1/0
device controllers, while a
wide range of memory deVices may be used from any s.ource. Thus, all required components can be
connected together in a very simple manner with virtually no other external logic. The user's effort then
becomes primarily one of software development. That is, the user can concentrate on describing his prob-
lem and translating it into a series of instructions that can be loaded into the microcomputer memory. Zilog
is dedicated to making this step of software generation as simple as possible. A good example of this is oUr