6800 Programming for Logic Design
By Adam Osborne
Copyright 1977


Introduction
------------

This book explains how an assembly language program within a microcomputer 
system can replace combinatorial logic- that is, the combined use of "off-the-
shelf," non-programmable logic devices, such as standard 7400 series digital 
logic.

If you are a logic designer, this book will teach you how to do your old job in 
a new way- by creating assembly language programs within a microcomputer 
system.

If you are a programmer, this book will show you how programming has found a 
new purpose- in logic design.

This is a "how to do it" book; as such, it has to become very specific, so a 
particular type of microcomputer, the MC6800, is referenced directly.

Companies manufacturing these microcomputers are:

Motorola. Incorporated
Semiconductor Products Division
3501 Ed Bluestein Boulevard
Austin, Texas 78721

American Microsystems
3800 Homestead Road
Santa Clara, California 95051


What This Book Assumes You Know

This book is a sequel to "An Introduction To Microcomputers," which was a 
single volume in its first edition, but is two volumes in its second edition.

"An Introduction To Microcomputers" describes microprocessors and 
microcomputers conceptually; it does not address itself to the practical matter 
of implementing a concept. This book addresses the practical matter of 
implementation.

In that this book is a sequel, it makes a single assumption- that you have 
read, or you otherwise understand the material covered in "An Introduction To 
Microcomputers". However, before launching into a real design project, you will 
need vendor literature that specifically describes the devices you have elected 
to use.

Note in particular that hardware and timing are not described in this book, 
either for the MC6800 CPU, or any other microcomputer devices; sufficient 
information may be found in "An Introduction To Microcomputers", Volume II- 
Some Real Products.

The MC6800 instruction set is described in Chapter 6 of this book, since 
programming is what this book is all about.


Understanding Assembly Language

Assembly language instructions are the transfer functions of a microcomputer 
system; taken together, they constitute an "instruction set," which describes 
the individual operations which the microcomputer can perform.

You define the events which must occur within the microcomputer system 
serially- as a sequence of instructions, which, taken together, constitute an 
assembly language program.

In reality, understanding what individual instructions do within a 
microcomputer system is very straightforward; it is one of the simplest aspects 
of working with microcomputers. Yet it unduly terrifies users who are new to 
programming. If that includes you, a word of advice - forget about mnemonics 
and instruction sets; take instructions one at a time as you encounter them in 
this book. When you do not understand what an instruction is doing, look it up 
in Chapter 6.

The specter of "programming" will haunt you only if you let it.


How This Book Has Been Printed

Notice that text in this book has been printed in boldface type and lightface 
type. This has been done to help you skip those parts of the book that cover 
subject matter with which you are familiar. You can be sure that lightface type 
only expands on information presented in the previous boldface type. Therefore, 
only read boldface type until you reach a subject about which you want to know 
more, at which point start reading the lightface type.


Table of Contents
-----------------

1) Introduction
2) Assembly Language and Digital Logic
3) A Direct Digital Logic Simulation
4) A Simple Program
5) A Programmer's Perspective
6) The MC6800 Instruction Set
7) Some Commonly Used Routines