Radio Shack TRS-80 Bedienungsanleitung

Catalog No 26-2103

Ita I

aeK

ADIVISION OF TANDY CORPORATION

One Tandy Center

Fort Worth, Texas 76102

SECOND EDITION

SECOND PRINTING -

1982

Reproduction

use,

without

express

permission, of editorial

pictorial

content.

any man-

ner.

prohibited.

patent

liability

assumed

with

respect

the

use

the

information

contained

herein.

iie every

precaution

has been

taken

the

preparation

this

book.

the

publisher assumes no responsibility for

errors

omissions. Neither

any liability assumed

for

damages resulting

from

the

use

the

information

con-

tained

herein.

Division

Tandy

Corporation,

Fort Worth, Texas 76102,

U.SA

Printed in the United States

America

Preface

We'd like to share acouple of important points before you get into this

book.

This Book was written for the technical person, by atechnical

person. It was not written to educate the average owner of a

TRS-80 Micro-computer. If you do not know what Hex

means.

how aNOR gate differs from aNAND

gate

...

you are not prepared to repair your Computer. (You

need some solid digital logictraining; and this Bookwon't give it

to you.)

If you are atechnical person, but have never played around

with microprocessors, dive right in! Acomputeris nothing more

than afast idiot. Don't let the "idiot" intimidate you. All of the

familiar logic is there; there just may be more of it than you're

used to seeing all

one place.

If you are ahobbyist who can convert Hex to Decimal

the

blink

an eye and you'veentered 16KBASIC languages using

front panel switches, then this book will probably appearlonger

than itneedsto be. All the information you seek is here; you will

justhaveto turn more pages to find

it.

2. We've incorporated alot of technical information that can lead

you right into the heart of the TRS-80 hardware. But we don't

wantyou to inferfrom this thatwe can make available engineer-

ing design services for your hardware/circuit ideas. We'd like

you to remember that any work you do on your TRS-80 "voids

the warranty". And, we will not obligate ourselves to repair or

correct owner-modifications.

So, once you open up the cabinet, you're on your own.

This bookhas been fun to write and we hope you havefun reading and

using it.

Mayall

your logic and software be glitch-free!

Table

Contents

Page

Introduction.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

System Block Diagram Description 9

The Memory Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

THEORY

OF OPERATION 14

CPU

Address Lines

CPU

Data

Bus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CPU

Control Group 18

System RAM 24

Video Divider Chain 28

Video

RAMs.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Video Processing

Keyboard 44

Input

and

Output

Port 44

System Power Supply 52

Level

II ROMs 55

ADJUSTMENTS

AND

TROUBLESHOOTING 57

THE OUTSIDE

WOR

LD 83

Memory Mapped External Device 86

Port

Based

External Device 88

Explanation

Expansion Port Signals. . . . . . . . . . . . . . . . . .

Connections

for

Expansion Port

Edge

Card

PARTS LIST 93

SCHEMATICS ,99

BASIC I ROMs 100

BASIC II ROMs 104

TRS-80

Master Schematic Diagram 111/113

Introduction

Armed with only aSchematic, attacking aTRS-80 Computer may at

first seem to be the ultimate exercise in futility. But that's where we

come in. This book has been written with those kinds of feelings in

mind (matter of fact, the writer went through many of the feelings of

trepidation as he was first asked to trouble-shoot and repair an early

TRS-80

...

You may know what

"CPU"

stands for. You may even

have some knowledge ofhow amicroprocessorsystem works.

Afterawhile, you find you have problems. You know a4K RAM needs

12 address lines. But you only find

You know acomputer keyboard

givesyou ASCII. Yet, you find the Keyboard is shorting out

address

line

adataline. You know howaTVtypewriterscrolls characters on

the screen, and you dofind the video memory wired to dothe job. But

where is all the hardwareto make the displayscroll?

You know what aNAND gate symbol looks like and you also know

what an

gate symbol looks like. But some sadist has gotten all his

symbols backwards. ANAND gate is shown like

OR gate, and the

gate looks like aNAND gate. To top it all off, the power supply

consists oftwo large rectangles with transistors and resistors sticking

out

them; and the onlyvoltages shown are the resulting outputs.

Welcome to the wonderful world ofcomputer electronics!

Now

admitit

...

you don'treally knowyourASCII from ascroll when it

comes to the TRS-80 Computer

...

and so once again we getbackto

this book. Join the crowd; line up and let's all learn together. Grab this

book, the Schematics and together we'll attack that TRS-80 with

soldering iron smoking.

The purpose of this book is to give you apractical knowledge of

system operation a'ia TRS-80. This book will show you why there are

only seven address inputs to a4K RAM. We'll show you when the

Microprocessor inputs data from the keyboard, the CPU thinks the

Keyboard is amemory, of all things! You'll learn how the CRT screen

is scrolled. (And you might even learn to appreciate the backward

symbolization!) As far as the Power Supply is concerned, you might

find that it's not nearly as complex as you thought. So, grab your

Schematics and let's take atourofthe TRS-80 Computer.

Let's start off easy

...

with a

...

System

BlockDiagram

The

integrated

circuits

contained

the

TRS-

80 can be

broken

down

into

about

major

sections. Figure 1shows

these

sections as

they

relate

other

sections.

The

heart

the

system

is definitely

the

CPU (Central Processing Unit).

You might

consider

the

CPU as being avery

dumb

calculator

circuit. It

may

dumb,

but

it's

afast

dummy.

Most

the

leads

the

CPU

Cire

data

linesand

address lines.

The

CPU tells

the

address bus

where

the

data

wants

located,

and

the

data

bus

agood place

for

the

informa-

tion

come

back

the

CPU.

The

address lines

are

outputs

from

the

CPU.

They

never receive

data

addresses from

other

sections.

The

data

lines

the

other

hand

can give

receive data.

ADAPTER

-=:::;

POWER

SUPPLY

DATA

READ

I----t>

DATA

OUT

CONTROL

CPU

WRITE

GROUP

ROM

OUT

ADDRESS

the

CPU has

the

heart

the

system,

the

ROM

(Read Only Memory)

could

be considered

the

brains.

The

ROM

tells

the

CPU

what

do,

how

and

where

put

after

it's

done.

Without

the

ROM,

the

CPU

would

just

sit

there

and

oscillate. When

power

first applied

the

system,

the

CPU has

just

enough

smarts

out-

put

an address

the

ROM

that

locates

the

CPU's first

instruction.

The

ROM

shoots

back

the

first

instruction

and

then

the

two

really

start

communicating.

less

than

second,

the

CPU,

under

ROM

supervision,

performs

all

the

house-

keeping necessary

get

the

system alive

and

"READY"

flashes

the

screen.

ROM

the

CPU misses

that

first piece

ROM

data,

then

may

go bananas. It

may

tell

the

ROM

that

ready

load a

tape

the

ROM

tells it

how

that.

The

Tape

Recorder

turns

on.

But

since

the

CPU

now

playing games

the

video

memory,

who

cares

about

the

tape?

The

CPU

operates

about

2MHz;

therefore,

digital

screw-ups seem

instantaneous.

Remember

that

the

CPU

the

work

horse

and

the

ROM

the

boss.

The

ROM

tells

the

CPU

how

it,

when

it,

and

where

put

it.

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