Radio Shack TRS-80 User manual

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TRS-BD ®
MOD . ELm
MICROCOMPUTER
Catalog Numbers 26-1061/1062/1063
I .
CUSTOM MANUFACTURED IN U.S.A. BY RADIO SHACKMA DIVISION OF TANDY CORPORATION

© Copyright 1980, Radio Shack, A Division of Tandy Corporation,
Fort Worth, TX 76102, U.S.A.
10 9 8 7 6 5 4 3 2

SECTION
NUMBER
II
Ill
IV
V
VI
TABLE OF CONTENTS
INTRODUCTION ............................ .
System Overview .......................... .
DISASSEMBLY/REASSEMBLY , ................. .
Disassembly .............................. .
Reassembly .............................. .
CPU CIRCUIT BOARD ......................... .
Technical Description ....................... .
Video Sync Circuits ......... , ............. .
Processor ............................. .
RAM ................................ .
Address Decoding ........................ .
Memory Map ........................... .
10 PO RT Description ..................... .
Video ................................ .
Keyboard ............................. .
Cassette Interface . . . . . . . . . . . . . . . . . . . . . . . . .
Line Printer and Real Time Clock ............. .
10 Bus ............................... .
Adjustments and Jumper Positions ............. .
Model 111 10 Bus Detailed Description .......... .
Model 111 PO RT Bits ...................... .
CPU Module Parts list . . . . . . . . . . . . . . . . . . . . . . . .
FLOPPY DISK INTERFACE .................... .
Technical Description ....................... .
Control and Data Buffering ................. .
Non-Maskable Interrupt Logic ............... .
Drive Select Latch and Motor On Logic ......... .
Wait State Generation and WAITIMOUT Logic .... .
Clock Generation Logic .................... .
Disk Bus Selector Logic .................... .
Read/Write Data Pulse Shaping Logic ........... .
Disk Bus Output Drives .................... .
Write Precompensation and Clock Recovery Logic .. .
Floppy Disk Controller Chip ................. .
Adjustments and Jumper Options ............. .
Floppy Disk Interface PC Board Parts List .......... .
RS-232C CIRCUIT BOARD ..................... .
RS-232C Technical Description ................ .
Pin-Out Description ...................... .
Port and Bit Assignments ..................... .
RS-232C PC Board Parts List .................. .
POWER SUPPLY ............................ .
Functional Specifications ..................... .
Troubleshooting ........................... .
Set-Up Procedures ......................... .
Visual Inspection . . . . . . . . .................. .
Start-Up ................................ .
No Output .............................. .
Performance Test .......................... .
Power Supply Component Values ............... .
PAGE
NUMBER
1
3
5
7
9
11
13
13
13
13
14
14
15
16
17
17
18
18
18
19
21
25
41
43
43
43
43
44
44
44
44
44
44
45
45
49
53
55
56
57
62
65
67
67
67
67
68
68
69
70

SECTION
NUMBER
VII
VIII
IX
TABLE OF CONTENTS (Cont'd)
VIDEO MONITOR ........................... .
Functional Specifications ..................... .
Service Adjustments ........................ .
ILLUSTRATED PARTS CATALOG
Illustrated Parts Catalog Parts List
MINI-DISK DRIVE .......................... .
General Description ........................ .
Introduction ........................... .
Important Notice ........................ .
Physical Description ...................... .
Functional Description .................... .
Interface Connections ..................... .
Physical Checkout ....................... .
Mounting the Disk Drive ................... .
Resistor Termination ...................... .
Flat Ribbon Cable Assembly ................. .
Theory of Operation ........................ .
Introduction ........................... .
Organization of the Disk Drive .......... : .... .
Functional Block Diagram Description .......... .
Index Pulse ................... - ......... .
Write Protect ........................... .
Track <.30 Switch ................ : ........ .
Spindle Drive ........................... .
Positioner Control ....................... .
Data Electronics ......................... .
Data Recording ......................... .
Data Reproduction ....................... .
Operation ............................... .
Interface Electronics Specifications ............ .
Input Control Lines ...................... .
SELECT Lines (DS1 * - DS4 *) ................ .
Drive Motor Enable (MOTORON) ............. .
Direction and Step (DIR*) (STEP*) ............ .
Compensated Write Data (CWD) .............. .
Write Enable (WG*) ...................... .
Side Select (SDSE L) ...................... .
Output Status .......................... .
Index Pulse (IP*) ........................ .
TRACK 00 (TRK0*) ...................... .
Write Protect (WPRT*) .................... .
Read Data (RD*) ........................ .
Maintenance . . . . . . . . . . . . . . . ................ .
Physical Description of the PC Boards ............ .
Circuit Board Test Points ..................... .
Option Select ............................. .
Input Line Terminations ................... .
Preventive Maintenance ...................... .
Cleaning the Head . . . . . . . . . . . . . . . . . . . . .... .
Alignment a~d Adjustment . ................... .
Drive Motor Maintenance ................... .
Carriage Movement Check .................. .
Head Radial Alignment/CE Alignment .......... .
Track <.30 Alignment ...................... .
Index Sector Adjustment ................... .
Head Amplitude/Compliance Check ............ .
PAGE
NUMBER
73
75
77
79
86
91
93
93
93
93
93
93
94
96
96
96
97
97
97
97
97
97
97
97
97
98
99
99
101
101
101
101
101
101
101
101
103
103
103
103
103
103
105
105
105
105
105
108
108
108
108
108
109
110
110
111

FIGURE
NUMBER
1
2
3
4
4
5A
58
5C
5D
5E
5F
5G
5H
5J
5K
1
2
2
3
SECTION
NUMBER
TABLE OF CONTENTS (Cont'd)
Final Check .............................. .
Disk Controller Board Parts List . . . . . . . . . . . . .... .
Servo Board Parts list (Non-Linear) ............. .
Servo Board Parts List (Linear) ................. .
Illustrated Parts Catalog Parts list ............... .
LIST OF ILLUSTRATIONS
TITLE
SECTION I - INTRODUCTION
PAGE
NUMBER
111
112
116
117
119
PAGE
NUMBER
TRS-80 Model 111 Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
SECTION 111 -CPU CIRCUIT BOARD
CPU Timing Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Video Timing Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
10 Bus Timing Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
CPU Printed Circuit Board -Component Side . . . . . . . . . . . . . . . . . . . . . 23
CPU Printed Circuit Board - Circuit Side . . . . . . . . . . . . . . . . . . . . . . . . 24
Model 111 CPU Schematic Diagram -
Video and Horizontal Sync Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Model 111 CPU Schematic Diagram -Processor Section . . . . . . . . . . . . . . . 32
Model 111 CPU Schematic Diagram -RAM Section . . . . . . . . . . . . . . . . . . 33
Model 111 CPU Schematic Diagram -
Address Decoding Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Model 111 CPU Schematic Diagram -Video Section . . . . . . . . . . . . . . . . . 35
Model 111 CPU Schematic Diagram -Keyboard Section . . . . . . . . . . . . . . . 36
Model 111 CPU Schematic Diagram -
Cassette Interface Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Model 111 CPU Schematic Diagram --
Line Printer and Real Time Clock Section . . . . . . . . . . . . . . . . . . . . . . . 38
Model 111 CPU Schematic Diagram -1/0 Bus Section . . . . . . . . . . . . . . . . 39
Model 111 CPU Schematic Diagram -
RS-232C Interface and FDC Interface Connections . . . . . . . . . . . . . . . . . 40
SECTION IV -FLOPPY DISK INTERFACE
FDC Board to CPU Board Signal Description . . . . . . . . . . . . . . . . . . . . . . 46
Floppy Disk Interface PC Board -Component Side . . . . . . . . . . . . . . . . . 47
Floppy Disk Interface PC Board - Circuit Side . . . . . . . . . . . . . . . . . . . . 48
Model 111 Floppy Disk Interface Schematic . . . . . . . . . . . . . . . . . . . . . . . 61

FIGURE
NUMBER
1
2
2
3
1
2
3
4
1
2
3
1
2
3
4
5
1
1A
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
18
19
20
20
LIST OF ILLUSTRATIONS (Cont'd)
TITLE
SECTION V - RS-232C CIRCUIT BOARD
PAGE
NUMBER
RS-232C Board to CPU Board Signal Description . . . . . . . . . . . . . . . . . . . 59
RS-232C PC Board - Component Side ..................... ·. . . . . 60
RS-232C PC Board - Circuit Side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Model 111 RS-232C Schematic Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . 63
SECTION VI -POWER SUPPLY
Test Set-Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
02 Collector Waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
02 Base Waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Power Supply Schematic Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
SECTION VII -VIDEO MONITOR
Video Monitor Printed Circuit Board . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Deflection Yoke Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Video Monitor Assembly Schematic Diagram . . . . . . . . . . . . . . . . . . . . . . 78
SECTION VIII - ILLUSTRATED PARTS CATALOG
Outer Case Assembly. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Case Top Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Base Plate Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Metal Chassis Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
Disk Drive Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
SECTION IX - FLOPPY DISK DRIVE
PC Board Component Locations (Logic Board) . . . . . . . . . . . . . . . . . . . . 94
PC Board Components Locations (Servo Boards) . . . . . . . . . . . . . . . . . . . 95
Resistor Termination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Cable Assembly - Connector Pin Removal Chart . . . . . . . . . . . . . . . . . . . 96
Functional Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
FM Recording . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Write Timing Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Read Timing Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Interface Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Logic Board Test Points and Connector Locations . . . . . . . . . . . . . . . . . . 106
Servo Board Connector Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
"Cat's Eyes" Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Radial Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Track 00 Stop Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
Index Sector Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
Index Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
Upper Arm and Carriage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Illustrated Parts Catalog -Exploded View . . . . . . . . . . . . . . . . . . . . . . . 118
Mini-Disk Drive Schematic (Sheet 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Mini-Disk Drive Schematic (Sheet 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
Servo Board Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
Mini-Disk Drive Schematic (new board) . . . . . . . . . . . . . . . . . . . . . . . . . 123
Mini-Disk Drive Schematic (new board) . . . . . . . . . . . . . . . . . . . . . . . . . 124

TABLE
NUMBER
1
2
1
2
LIST OF TABLES
TITLE
SECTION V - RS-232C CIRCUIT BOARD
PAGE
NUMBER
B RG Programming Table . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . 55
SECTION VI -POWER SUPPLY
Load Board Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Voltage and Ripple Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
SECTION IX - MINI-DISK DRIVE
Interface Connector Pin Assignments . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Power Connector Pin Assignments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

1

SYSTEM OVERVIEW
The Radio Shack TRS-80 Model 111 Microcomputer is an enhanced version of Radio Shack's popular TRS-80 Microcom-
puter (Model I). The TRS-80 Model Ill is software compatible with the Model I so that owners of either system can take
advantage of the large number of programs available.
Features of the TRS-80 Model 111 which are common to the TRS-80 Model I include:
• Availability of Level I or Level 11 BASIC in ROM
• Full size typewriter style keyboard
• A 12-inch video display
• Built-in cassette interface
• Character display of 16 lines of 64 characters
• Graphics under control of BASIC (128 H x 48 V)
• UL recognized construction
In addition, the Model 111 has the following standard features:
• 12-key numeric keypad for rapid entry of numbers
• Rugged cabinet housing keyboard, electronics, video display, and power supply
• Direct drive video monitor for improved resolution
• Internal power supply
• Parallel printer port for use with Radio Shack printers
Several other features are available when Level II BASIC is used; features such as: real time clock, upper and lower case
characters, RAM internally expandable to 48K bytes, 1/0 port for peripheral expansion, and cassette interface available
with 500 and 1500 baud rates.
Optional peripherals for the TRS-80 Model Ill include disk drives (two built-in, two external) with double density for
increased storage capacity, and a built-in RS-232 serial interface for communications and peripheral interface.
The Block Diagram shows the various internal components and connections of the Model 111 Microcomputer.
3

~
TO
EXTERNAL
DISKS
FLOPPY
DISK
CONTROLLER
(optional)
DISK #0
(optional)
DISK #1
(optional)
RS-232
1/0
LINE
PRINTER
PORT
Z-80
1/0 BUS
4K or 14K ROM
4K, 16K, 32K, or 48K RAM
REAL TIME CLOCK
UPPER/LOWER CASE VIDEO
500/1500 BAUD CASSETTE INT.
KEYBOARD INTERFACE
LINE PRINTER INTERFACE
1/0 BUS INTERFACE
FIGURE 1. TRS-80 MODEL Ill BLOCK DIAGRAM
POWER
SUPPLY
BRIGHTNESS
AND
CONTRAST
POWER
Ir
l
POWER
SUPPLY
(optional)

I
5

-

DISASSEMBLY
CASE:
1. Remove all cables from the bottom and rear of the Com-
puter. Position the Computer on its rear panel to provide
easy access to the case bottom. Remove the ten screws
from the case bottom. Notice the different types and
lengths of screws and note their positions. Set them
aside in groups.
2. Position the Computer upright and remove the #6 screw
and washer from the top of the back panel of the case.
3. Very carefully remove case top, lifting striaght up and
setting it aside to the left (if facing video screen). Be
careful not to exceed the length of the video cable.
4. Remove screws from the chassis shield and the ground
connectors and remove the shield. **
CPU BOARD:
1. Remove all cables connecting the CPU Board (power
supply cable, video, keyboard, and cassette cables, and
if applicable, the RS-232 and FDC inter-connect cables).
2. Remove the five screws fastening the PC Board (two in
upper right corner, three on bottom).
3. Remove the small PCB Mount Bracket and its two
screws from atop the metal chassis bracket. **
4. Make sure all cables to the CPU Board have been d iscon-
nected then remove the Board. (If your unit uses plastic
spacer mounts to hold the Board, press the small tabs on
the mounts through the mounting holes in the PCB and
gently pull the CPU Board off.)
FDC BOARD (optional):
NOTE: The CPU Board must be remove before removing the
the FDC Board.
1. Be sure to disconnect all cables to the FDC Board.
2. Remove the screws holding the FDC Board to the metal
chassis and remove the Board.
* *Not applicable to all units.
RS-232 BOARD (optional):
NOTE: The CPU Board must be removed before removing
the RS-232 Board.
1. Be sure to remov~ all cables connecting the RS-232
Board.
2. Remove the screws connecting the PC Board to the
chassis and remove the Board.
MAIN POWER SUPPLY:
1. Remove all interconnect cables to the Boards fastened
on the metal chassis brac::ket (power supply cable,
video, keyboard, and cassette cables, and if applicable,
RS-232 and FDC power connectors and the Disk ribbon
cable).
2. Remove the four screws fastening the metal chassis
bracket to the case bottom.
3. Make sure all inter-connecting cables are removed, then
carefully lift out chassis bracket and attached Boards.
4. Remove the four screws fastening the Power Supply to
the Bracket (notice where the ground tab is fastened),
then carefully remove the power supply.
DISK DRIVE POWER SUPPLY (optional):
1. Disconnect all cables and wires connecting to the Power
Supply.
2. Remove the four screws fastening the Board to the Disk
Mounting Bracket (notice where the ground tab is fas-
tened), then carefully remove the Power Supply.
DISK DRIVES (optional):
1. To remove the Disk Drive in the top position, carefully
remove the FDC inter-connect cable connected to the
rear of the Drive.
2. Remove the four screws and washers (two on each side)
which connect the Drive to the Disk Mounting Bracket.
3. Disconnect the power supply connector from the bot-
tom of the top board in the Disk Drive and also remove
the ground wire from the rear of the Drive.
7

4. To remove the Disk Drive in the bottom position, you
must first remove the Disk Drive Power Supply.
5. After removing the Power Supply, remove the FDC
inter-connect cable from the rear of the Drive.
6. Remove the four screws and washers (two on each side)
which connect the Drive to the Disk Mounting Bracket.
7. Disconnect the power supply connector from the bot-
tom of the top board in the Disk Drive and also remove
the ground wire from the rear of the Drive.
VIDEO MONITOR (CRT) AND VIDEO BOARD
1. Disconnect the four color coded wires with spade lugs
from the CRT yoke. (Be sure to note their positions.)
2. Disconnect the connector on the rear of the CRT neck.
WARNING
There may be a high voltage charge on the high voltage
anode. To discharge, connect one end of a wire to a
known good ground and connect the other end of the
wire to the blade of a common screwdriver. Insert the
screwdriver blade under the suction cup and touch it
to the clip holding the wire to the CRT.
8
3. Insert a common screwdriver under the suction cup on
the high-voltage anode wire on the side of the CRT. Use
the screwdriver to compress the clip holding the wire to
the tube and pull the wire free.
4. Remove the ground wire fastened directly to the Video
Board.
5. Remove the upper right and l't>wer left nuts and washers
which hold the CRT in place.
CAUTION
If dropped, the CRT may implode. To avoid this kind of
accident, support the CRT while performing the next
step.
6. Remove the remaining l~wer right and upper left nuts,
and washers and carefully remove the CRT.
7. Disconnect the CPU cable connector from the Video
Board.
8. Remove the two screws fastening the Video Board to the
Case Top and carefully lift out Board.

REASSEMBLY
RS-232 BOARD (optional):
1. Install the PC Board using #6 x 3/8" screws. If appli-
cable, press the PC Board onto the plastic spacer mounts
then fasten with the screws.
2. Reconnect all cables to the RS-232 Board.
FDC BOARD (optional):
1. Install the PC Board using #6 x 3/8" screws and the
plastic spacer mounts, if used.
2. Reconnect all cables to the FDC Board.
CPU BOARD:
1. Make sure good insulating washers are attached to the
CPU Board (Rev. F boards only) then fasten the Board
using #6 x 1 /4" screws.
2. Reconnect all cables to the CPU Board (power supply
cable, video, keyboard, and cassette cables, and if appli-
cable, RS-232 and FDC inter-connect cables).
3. Attach the small PCB Mount Bracket (if used) to the
metal chassis bracket with two #6 x 1 /4" screws.
MAIN POWER SUPPLV:
1. Fasten the Power Supply to the metal chassis bracket
using four #6 x 1/4" screws. Be sure the ground tab is
fastened back in place.
2. Install the chassis bracket (with all Boards in place) in
the case bottom using four #6 x 1 /4" screws.
3. Reconnect all cables (power supply, video, keyboard,
and cassette cables, and RS-232 and FDC power cables
and Disk ribbon cable if necessary).
DISK DRIVE (optional):
1. Place the Disk Drive in the bottom position and recon-
nect the ground wire and power supply connector.
2. Fasten the Drive with four #6 x 1 /2" screws and four
flat washers (two on each side).
3. Reconnect the FDC inter-connect cable to the rear of
the Drive.
4. Position the second Disk Drive in the top position and
reconnect the ground wire and power supply connector.
5. Fasten with four screws and washers (two on each side).
6. Reconnect the FDC inter-connect cable to the rear of
the Drive.
DISK DRIVE POWER SUPPLV (optional):
1. Before installing the Power Supply, be sure that the
bottom Disk Drive is mounted in place and the Disk
Shield is in positon on the Disk Mounting Bracket.
2. Reconnect all cables and wires to the Power Supply.
3. Fasten the Power Supply with four #6 x 3/8" screws.
Be sure the ground tab is fastened back in place.
VIDEO MONITOR (CRT) AND VIDEO BOARD:
1. Position the CRT in the Case Top and install the upper
left and lower right #10 washers and nuts.
2. Install the upper right and lower left #10 washers and
nuts. Be sure to reconnect the ground wire from the
CPU cable. It will require two nuts to fasten it.
3. Install the Video Board into the Case and fasten with
two #6 x 1 /4" screws.
4. Connect the ground wire with solder lug back to the
Video Board.
5. Install the plug on the rear of the CRT neck.
6. Install the four color coded wires with spade lugs to
their associated terminals (as determined by a colored
dot on the yoke near each terminal).
7. Install the high-voltage anode wire on the side of the
CRT. Use a screwdriver to compress the clip and insert
it into the CRT. Press down on the suction cup to
secure.
CASE:
1. Double-check to be sure all wires are connected cor-
rectly and all Boards are properly fastened.
2. Attach the chassis shield (if used) with #6 x 1/4"
screws and reconnect the ground connectors.
3. Carefully place the Case Top over the Case Bottom.
Do not hit the CRT neck. It could implode or break
off.
4. Install the #6 x 3/8" sheet metal screw and flat washer
in the top rear panel of the Case.
5. Carefully rest the Computer on its rear panel and replace
the ten #8 screws; five 1" sheet metal toward rear, three
7 /8" machine head along front, and two 1" machine
head in remaining positions.
9

11

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