Radio Shack TRS-80 Product manual

CUSTOM MANUFACTURED NUSA BV RADIO SHACK §ADIVISION OF TANDY CORPORATION

kTM
TRS-80
COLOR
COMPUTER
TECHNICAL
REFERENCE
MANUAL
Radio Jhaek R
Ma DIVISION OF TANDY corporation
FORT WORTH. TEXAS 76102

Color Computer Technical Reference Manual:
Copyright ©1981 Tandy Corporation,
Fort Worth, Texas 76102, U.S.A.
All rights reserved.
Portions of this manual were reproduced, with express
written permission from the Motorola Corporation, from
the following Motorola data sheets:
Reproduction or use, without express written permission
from Tandy Corporation, of any portion of this manual, is
prohibited. While reasonable efforts have been taken in
the preparation of this manual to assure its accuracy,
Tandy Corporation assumes no liability resulting from any
errors or omissions in this manual or from the use of the
information obtained herein.
ADI-492R2
ADI-847
ADI-595
DS9435R1
DS-9522
MC6847
MC6809E
MC6883
MC6821
MC1372
This manual was written by Dale Chatham,
and edited by Sandra Williams
Printed in the United States of America

IMPORTANT NOTICE
This Technical Reference Manual is written for owners of the TRS-80 Color
Computer, who have athorough understanding of electronics and computer
circuitry. It is not written to the beginner's level of comprehension.
Radio Shack will not be liable for any damage caused, or alleged to be
caused, by the customer or any other person using this technical manual to
repair, modify, or alter the TRS-80 Color Computer in any manner.
Many parts of the computer electronics are very sensitive and can be easily
damaged by improper servicing. We strongly suggest that for proper servicing,
the computer be returned to Radio Shack.
Because of the sensitivity of computer equipment, and the potential
problems which can result from improper servicing, the following limitations
apply to services offered by Radio Shack:
1
.
If any of the warranty seals on any Radio Shack computer product are
broken. Radio Shack reserves the right to refuse to service the equipment
or to void any remaining warranty on the equipment.
2. If any Radio Shack computer equipment has been modified so that it is
not within manufacturer's specifications, including, but not limited to,
the installation of any non-Radio Shack parts, components, or replace-
ment boards, then Radio Shack reserves the right to refuse to service the
equipment, void any remaining warranty, remove and replace any
non-Radio Shack part found in the equipment, and perform whatever
modifications are necessary to return the equipment to original factory
specifications.
3. The cost for the labor and parts required to return the Radio Shack
computer equipment to its original specifications will be charged to the
customer in addition to the normal repair charges.

TABLE OF CONTENTS
SECTION PAGE
NUMBER NUMBER
IINTRODUCTION 1
System Description 2
System Block Diagram —Illustration 3
Memory Map 4
II DISASSEMBLY/ASSEMBLY 11
Disassembly 12
Reassembly 12
Disassembly/Reassembly —Illustration 13
III THEORY OF OPERATION 15
6809E CPU 16
6809E Block Diagram —Illustration 16
6809E Programming Model —Illustration 17
6809E Typical Timing of Read/Write Cycles —Illustration 18
Reset Circuit 17
Dynamic Memory Control 19
MC6883 Block Diagram —Illustration 20
Timing Diagram —Illustration 21
ROM 21
Video Interface 21
Mode Selection —Table 124
Description of Display Modes —Table 225
Display Character Set —Table 327
VDG Video Output —Illustration 28
MC1372 Block Diagram —Illustration 28
Video Input to the Modulator —Illustration 29
PIA's 29
PIA Block Diagram —Illustration 29
Digital to Analog (D/A) 30
Joystick Interface 30
Sound Output 31
Sound Selection —Table 431
Sound Circuity —Illustration 31
Cassette Interface 32
Sample Data of Cassette Format —Illustration 32
Tape Format Information 32
RS-232C Interface 33
RS-232 Connector Pin-out —Illustration 33
Keyboard Interface 33
System Power Supply 33
723 Regulator Block Diagram —Illustration 34
Cartridge ROM and Other Devices 35
Cartridge Connector Signals —Table 536
ROM Cartridge Board Schematic —Illustration 37
RS-232 Devices 38
Line Printer Variables —Table 638
Alternate Line Printer Variables —Table 739
Joysticks 40
Joystick Schematic —Illustration 40
TV Switch Box 41
Antenna Switch Box Schematic —Illustration 41

TABLE OF CONTENTS (cont'd)
SECTION PAGE
NUMBER NUMBER
IV TROUBLESHOOTING 43
Fault Isolation 44
Diagnostic Notes 44
Video interface 44
Joystick Interface 45
Cassette Interface 45
Keyboard Interface 45
RS-232 Interface 45
Power Supply 46
Power Supply Voltage Levels —Illustration 47
VPARTS LISTS 49
Printed Circuit Board Parts List 50
Illustrated Parts Breakdown 56
Illustrated Parts Breakdown —Illustration 57
VI PRINTED CIRCUIT BOARD 59
Printed Circuit Board —Component Side 60
Printed Circuit Board —Circuit Side 61
VII SCHEMATIC 63
Color Computer Schematic —Sheet 164
Color Computer Schematic —Sheet 266
Color Computer Schematic —Sheet 368

SECTION I
INTRODUCTION

SYSTEM DESCRIPTION
The primary functions of the Color Computer are performed
by five 40-pin Large Scale Integration (LSI) chips plus
Random Access Memory (RAM) and Read Only Memory
(ROM). These five chips are indicated on the Block Diagram
(Figure 1) by CPU, SAM, VDG, and two PIA's. With only
these five chips plus RAM, ROM, and apower supply, the
Color Computer would operate and provide acomposite video
output. However, to allow communication with the outside
world, I/O interfaces must be added.
The main component of any computer system is the Central
Processor Unit (CPU). It is the duty of the CPU to provide or
request data and select the proper address for this data. In
addition, the CPU is capable of performing alimited set of
mathematical and logical operations on the data.
ROM has the duty of providing the CPU with apredefined set
of instructions. Without ROM, the CPU would run wild and
randomly execute instructions. In normal operation, the CPU
jumps to the start address in ROM after the reset switch has
been pressed, and then performs the reset program to set up
all of the programmable devices. Following this, the BASIC
instruction set residing in ROM is in control of the CPU.
RAM provides storage for the programs and/or data currently
being executed. In addition, this same RAM is used to generate
the video display. Normally, no conflict will be observed
because the program will use one portion of RAM and the
display will use another. During normal usage, the BASIC
interpreter located in ROM will control the execution of
programs located in RAM.
Acentral component in the Color Computer is the dynamic
RAM controller chip (SAM). This chip provides refresh and
address multiplexing for the RAM. It also provides all of the
system timing and device selection.
The video display generator (VDG) provides virtually the
entire video interface on one chip, and allows several different
alphanumeric and graphic modes. This mode of operation of
the VDG is controlled by one of two peripheral interface
adapters (PIA's) used in the Color Computer. With this
information and RAM data, the VDG generates composite
video and color information for the modulator circuitry.
The remaining circuitry in the Color Computer is devoted to
Input/Output (I/O) communication. The most important part
of this circuitry is the keyboard which allows the operator to
enter information. Other I/O circuits are provided to allow
joystick inputs, cassette input and output, and RS232 input
and output.

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