Tandy 102 User manual

TANDY® of
00•
CUSTOMMANUFACTUREDFORRADIOSHACK,ADIVISIONOFTANDYCORPORATION

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CONTENTS
PART I. INTRODUCTION ........................................................................................ 1-1
System Overview ............................................................................................. 1-2
External View.................................................................................................... 1-2
Internal View..................................................................................................... 1-5
Specifications................................................................................................... 1-7
PART 11.DISASSEMBLY INSTRUCTIONS............................................................. 2-1
Cases ................................................................................................................. 2-1
Keyboard and LCD PCBs................................................................................. 2-1
Main PCB........................................................................................................... 2-2
PART III. MAINTENANCE .......................................................................................3-1
To clean the body and LCD display ................................................................ 3-1
PART IV. THEORY OF OPERATION ....................................................................... 4-1
General .............................................................................................................. 4-1
Block Diagram .................................................................................................. 4-2
CPU .................................................................................................................... 4-3
Memory ............................................................................................................. 4-3
I/O Map ............................................................................................................. 4-5
Keyboard .......................................................................................................... 4-6
Cassette Interface Circuit ............................................................................... 4-7
Printer Interface Circuit ................................................................................... 4-8
Bar Code Reader Interface Circuit ................................................................. 4-9
Buzzer Control Circuit ...................................................................................... 4-10
System Bus ....................................................................................................... 4-11
Clock Control Circuit ....................................................................................... 4-12
Serial Interface Circuit ..................................................................................... 4-14
LCD .................................................................................................................... 4-21
Power Supply Circuit ....................................................................................... 4-24
PART V. TROUBLESHOOTING .............................................................................. 5-1
General Guidance ............................................................................................ 5-1
Troubleshooting Guide.................................................................................... 5-1
Check List......................................................................................................... 5-11

PARTVI. EXPLODEDVIEW/PARTS LIST............................................................. 6-1
Electrical Parts List..........................................................................................6-2
Mechanical and Assembly Parts List ............................................................. 6-11
PART VII. SCHEMATIC DIAGRAMS/PCBVIEWS ................................................ 7-1
Schematic Diagrams........................................................................................7-1
PCBViews......................................................................................................... 7-3
APPENDIX A/ INSTALLATION ............................................................................A-1
Installation of Optional RAMand ROM ..........................................................A-1
APPENDIX B/ KEYBOARDLAYOUT, CONNECTOR PIN
ASSIGNMENTS AND CHARACTER CODE TABLE ....................... B-1
B-1. Keyboard Layout.....................................................................................B-1
B-2. Connector PinAssignments................................................................... B-2
B-3. Character Code Table.............................................................................B-7
APPENDIX C/ TECHNICAL INFORMATION ..........................................................C-1
C-1. 80C85A ....................................................................................................C-1
C-2. 81C55 .......................................................................................................C-7
C-3. 6402 .........................................................................................................C-13
C-4. BasicConstructionof LCD.....................................................................C-19
io

List of Illustrations
FIGURE DESCRIPTION PAGE
NUMBER NUMBER
1-1 Front View................................................................................................................................ 1-2
1-2 Rear View ................................................................................................................................ 1-3
1-3 Bottom View ............................................................................................................................ 1-4
1-4 Main PCB (Bottom View)....................................................................................................... 1-5
1-5 LCD PCB ................................................................................................................................. 1-6
2-1 Top Case Removal ................................................................................................................. 2-1
2-2 Keyboard and LCP PCBs Removal ....................................................................................... 2-1
2-3 Main PCB Removal ................................................................................................................. 2-4
4-1 Organization of Section IV ..................................................................................................... 4-1
4-2 System Block Diagram ........................................................................................................... 4-2
4-3 Functional Block Diagram of Bus Separation Circuit ........................................................... 4-3
4-4 Memory Map ........................................................................................................................... 4-3
4-5 Address Decoding and Bank Selection Circuit .................................................................... 4-4
4-6 I/O Address Decoding Circuit ................................................................................................ 4-5
4-7 Condition of Pressing "T" Key ............................................................................................... 4-6
4-8 Cassette Interface Circuit ....................................................................................................... 4-7
4-9 Printer Interface Circuit .......................................................................................................... 4-8
4-10 Bar Code Reader Interface Circuit ........................................................................................ 4-9
4-11 Buzzer Control Circuit ............................................................................................................ 4-10
4-12 Time Set Sequence ofuPD1990AC ....................................................................................... 4-12
4-13 Time Read Sequence ofuPD1990AC ................................................................................... 4-13
4-14 Functional Block Diagram of the Serial Interface ................................................................. 4-14
4-15 RS-232C/MODEM Selection Circuit ...................................................................................... 4-15
4-16 RS-232C Interface Circuit ...................................................................................................... 4-16
4-17 MODEM IC and Peripheral Circuit ......................................................................................... 4-17
4-18 Transmission Filter Circuit ..................................................................................................... 4-17
4-19 Reception Filter Circuit ........................................................................................................... 4-18
4-20 MODEM Adjustment ............................................................................................................... 4-19
4-21 MODEM Connector Interface Circuit .................................................................................... 4-20
4-22 HD44103 Internal Logic Diagram .......................................................................................... 4-21
4-23 HD44102 Internal Logic Diagram .......................................................................................... 4-22
4-24 LCD Waveform ........................................................................................................................ 4-23
4-25 Power Supply and Reset Circuit ............................................................................................ 4-25
6-1 Exploded View ........................................................................................................................ 6-1
7-1 Main PCB - Schematic Diagram ............................................................................................ 7-1
7-2 LCD PCB- Schematic Diagram ............................................................................................ 7-2
7-3 Main PCB - Top View ............................................................................................................. 7-3
7-4 Main PCB - Bottom View........................................................................................................ 7-4
7-5 LCD PCB - Top View .............................................................................................................. 7-5
A-1 Installation of RAM and ROM ................................................................................................. A-1
B-1 Keyboard Layout .................................................................................................................... B-1
B-2 System Bus Connector ........................................................................................................... B-2
B-3 RS-232C Connector ............................................................................................................... B-3
B-4 Printer Connector ................................................................................................................... B-4
B-5 Cassette Connector ................................................................................................................ B-5
B-6 MODEM Connector ................................................................................................................ B-5
B-7 Bar Code Reader Connector ................................................................................................. B-6
C-1 Functional Block Diagram ......................................................................................................C-1
C-2 Pin Configuration of 80C85A ................................................................................................. C-1
C-3 Trap and RESETIN ................................................................................................................. C-5
C-4 80C85A Basic System Timing ...............................................................................................C-7
C-5 Functional Block Diagram ..................................................................................................... C-7
iii

FIGURE DESCRIPTION
NUMBER NUMPAGEBER
..................................
C-6 Pin Configuration of 81C55 .................................................................. C-7
C-7 Internal Register of 81C55 .....................................................................................................C-9
C-8 Programming the Command/Status Register ...................................................................... C-10
C-9 Reading the C/S Register .......................................................................................................C-11
C-10 Bit Assignments to the Timer Counter .................................................................................. C-11
C-11 Functional Block Diagram ......................................................................................................C-13
C-12 Pin Configuration of 6402.......................................................................................................C-13
C-,13 Receiver Timing .....................................................................................................................C-16
C-14 Transmitter Operation ............................................................................................................C-17
C-15 Start Bit Detection Timing ......................................................................................................C-18
C-16 Construction of LCD Panel ....................................................................................................C-19
C-17 Operation Theory of LCD Panel.............................................................................................C-20
Listof Tables
TABLE
NUMBER DESCRIPTION NUMPAGEBER
4-1 I/O MAP ................................................................................................................................... 4-5
4-2 Port Address of PIO................................................................................................................ 4-5
4-3 System Bus Pin Assignments ................................................................................................ 4-11
B-1 System BusConnector PinAssignments............................................................................. B-2
B-2 RS-233C Connector PinAssignments.................................................................................. B-3
B-3 Printer Connector Pin Assignments ...................................................................................... B-4
C-1 InterruptPriority, RestartAddress and Sensitivity............................................................... C-4
C-2 80C85A Machine Cycle Chart ...............................................................................................C-6
C-3 80C85A Machine State Chart ................................................................................................ C-6
C-4 I/O Address of 81C55.............................................................................................................C-9
C-5 Port ControlAssignment........................................................................................................C-10
C-6 Control Word Format ..............................................................................................................C-15
iv

I. INTRODUCTION
This manual is prepared for the Tandy 102 technicians working in field or in repair centers. Users of
this manual should be acquainted with the 80C85A microprocessor, the 81 C55 PIOand the 6402
UART. Ifyou need more detailed information,referto Appendix C inthis manual.
This manual consists of seven sections and three appendices:
Section I
This section provides general information on the Tandy 102 such as specifications, external
views and internal views.
Section II
This section describes the disassembly procedures.
Section III
This section describes the maintenance of the Tandy 102.
Section IV
This section describes the general theory of operation for the Tandy 102.
SectionV
This section describes how to troubleshoot the Tandy 102.
Section VI
This section provides an exploded view and parts list of the Tandy 102.
Section VII
This section provides the schematics, PCB diagrams, and silkscreen views of the PCBs of the
Tandy 102.
Appendix A
This appendix provides instructions for installing the optional ROM and additional RAMs.
Appendix B
This appendix provides the character code table, keyboard layouts and connector pin
assignments.
Appendix C
This appendix provides the technical information of the 80C85A, 81 C55, 6402 and LCD.

SystemOverview
Tandy 102 portable computer is a low cost version of the Radio Shack TRS-80 Model 100 Portable
Computer. The Tandy 102 is fully compatible with the Model 100 in its software so that both system
users can take advantage of the large number of programs available.
The Tandy 102 has the following applications programs in the standard ROM: BASIC, TEXT,
TELCOM, ADDRSS, SCHEDL and TELCOM.
External View
1 Keyboard: Can be used like the standard typewriter. However, the Tandy 102 does have a few
speciatkeys. (See Appendix B of this manual for more details.)
2 LCD Screen: The Tandy 102 display has eight lines that allow 40 characters on each line.
3 Power Switch: Move this switch towards the front to turn the power on. To conserve the
batteries, the Tandy 102 automatically turns the power off ifyou do not use it for 10 minutes in
default setting.
4 Low Battery Indicator: Before the Tandy 102 is operational batteries become exhausted, this
indicator will illuminate.
5 Display Adjustment Dial: This control adjusts the contrast of the LCD display relative to the
viewing angle.
6 External Power Adapter Connector: Connect the appropriate and of Radio Shack's AC Power
Supply (Catalog Number 26-3804, optional/extra) to this connector. Connect the other end of
the power supply to a standard AC wall-outlet or approved power strip.
1 Keyboard 2 LCD Screen 4 Low Battery
Indicator
11-111-1
1-1
N, 11-1
ZZ
6 ExternalPower Adapter
Connector
5 Display Adjustment
Dial
3 Power Switch
Figure 1-1. Front View
1-2

1 RESETSwitch: Ifthe Tandy 102 "locks up" (i.e., the display "freezes" and all keys seem to be
inoperative), press this button to return to the Main Menu (start-up). It is not likely that the
Tandy 102 will lock-up when you are using the built-in applications programs, however, it may
occur with customized programs.
2 RS-232C Connector: Attach a DB-25 cable (such as Radio Shack Catalog Number 26-1408) to
this connector when you need to receive or transmit serial information. When you
communicating directly with another TRS-80 computer, a Null MODEM Adapter (26-1496) is
required. An 8" Cable Extender (26-1497) may also be required.
3 SYSTEM BUS Connector: Connect this connector to the TRS-80 Disk/Video interface
(26-3806), using the system bus cable.
4 PRINTER Connctor: For hard-copy printouts of information, attach any Radio Shack parallel
printer to this connector, using an optional/extra printer cable.
5 Direct-Connect MODEM (PHONE)Connector: When communicating with another computer via
the Tandy 102's built-in MODEM, connect the round end of the optional/extra MODEM cable
to this connector.
6 CASSETTE Recorder Connector: To save or load information, on a cassette tape, connect the
cassette recorder here. An optional/extra cassette recorder (and cable) is required.
7 Bar Code Wand Connector: Attach the optional/extra bar code wand to this connector. Note
that special bar code reader software is required.
8 DIR/ACP Selector : This selector allows you to select either a direct or acoustic coupler
connection. Ifyou are communicating with another computer over the phone lines via the
built-in, direct-connect MODEM, set this switch to the DIR position. If you are using the
optional/extra Model 100 Acoustic Coupler (26-3805), set this connector to the ACP position.
9 ANS/ORIG Selector: Ifyou are "originating" a phone call to another computer, set this switch
to ORIG. If another computer is calling your Tandy 102, set to ANS.
5 Direct-Connect
MODEM (PHONE) Connector
6 CASSETTERecorder
Connector
4 PRINTERConnector
3 SYSTEM BUS Connector
1 RESETSwitch
2 RS-232C Connector
Figure 1-2. Rear View
9 ANS/ORIG Selector
8 DIR/ACP Selector
7 Bar Code Wand
Connector
1-3

1 MEMORY POWERSwitch: This switch is used to prevent discharge of the internal
Nickel-Cadmium battery, which is used for RAM back-up. The Tandy 102 will operate only
when the power switch is set to ON. Set this switch to the OFF position when the Tandy 102 will
not be used for a long period of time. Note that the RAM will not be backed up when this switch
is set to the OFF position.
2 Optional ROM and RAM Compartment: An optional/extra ROM and RAM can be inserted into
this compartment to enhance the Tandy 102 capabilities.
3 Battery Compartment : When not connected to an AC power source, the Tandy 102 gets its
power from four AA size batteries that must be installed in this compartment.
3 BATTERYCompartment
1 MEMORY POWER 2 OPTIONAL ROM and RAM
Switch Compartment
XX
11
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Figure 1-3. Bottom View

Internal View
The Tandy 102 consists of three printed circuit boards:
• LCD PCB
• Keyboard PCB
• Main PCB
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Specifications
Main Components
Keyboard
Life of key switch
Number of keys
Function keys
Caps/NUM lock key
Other keys
LCDdisplay
Display panel
Dot pitch
Dot size
Effective display area
Operation batteries
Batteries
Operation time
Memoryprotection battery (On Main PCB)
Battery
Back-up time
Recharge method
Charging current
LSIs
CPU
ROM
RAM
Power consumption
Dimensions
Weight
72 keys (8 x 9 key matrix)
3 millionskeystrokes
0.5 millionkeystrokes
5 millionskeystrokes
240 x 64 full-dot matrix
1/32duty
1/6.66bias
0.8 x 0.8 mm
0.73x0.73 mm
191.2(W) X 50.4(D) mm
Four type AA
Alkaline-manganese batteries
5 days (Typ.) - 4 hours per day
20 days (Typ.) - 1 hour per day
(Note: without I/O units at normal temparature)
Rechargeable battery (50mAh/3.6V)
More than 20 days-16 KB RAM
More than 10 days-32 KB RAM
Trickle charge by AC adapter
operation batteries
1.2 mA (Typ.)
80C85A
Code and pin compatible with 8085
Maximum 64 KB
Standard 32 KB
Optional 32 KB
Maximum 32 KB
Standard 24 KB
Optional 8 KB
65 mA (Typ.)
11-3/4" (W) X 8-1/2"(D) X 1-1/2" (H)
300 (W) X 215 (D) X 38.5 (H) mm
3 lbs. 2 oz.(withbatteries)
1.4 kg

I/O Interface
RS-232C
Conforms to EIAstandard signal
Communications protocol
Word length
Parity
Stop bit length
Baud rate
Maximum transmission distance
Maximum driver output voltage
Minimum driver output voltage
Maximun receiver input voltage
Minimum receiver input vltage
MODEMICoupler
Conforms to BELL 103 Standard
Data length
Parity
Stop bit length
Baud rate
Full duplex
Transmit output level
Receive sensitivity
Other functions
Printer interface
Conforms to Centronics interface standards
Handshake signals
Audio cassette interface
Data rate
Input level
Output level
Barcodereaderinterface
Input level
TXR (Transmit Data)
RXR(Receive Data)
RTS(Request to Send)
CTS (Clear to Send)
DSR (Data Set Ready)
DTR (Data Terminal Ready)
6, 7, or 8 bits
NONE, EVENor ODD
1 or 2 bits
75, 110, 300, 600, 1200, 2400,
4800, 9600 or 19200 BPS
5 meters
± 5 volts
±3.5 volts
± 18 volts
± 3 volts
6, 7 or 8 bits
NONE, EVENor ODD
1 or 2 bits
300 BPS
Answer mode/originate mode switchable
15 dBm ± 2dBm
-30 dBm
Hang-up function
Auto pulse dialing function
10/20 PPS
STROBE, BUSY, BUSY
1500 BPS
(Mark 2400 Hz, Space 1200 Hz)
0.8 to 5 volts (Peak to peak)
580 mV ± 10%
3.5 volts (Min.)-High
1.5 volts (Max.)-low

II. DISASSEMBLYINSTRUCTIONS
Cases
1. Disconnect the cables from the unit.
Taking care not to scratch the LCD screen and key tops, turn the unit over and remove 4 screws
A from the upper and lower cases.
2. Remove the upper case.
Therefore, the upper and lower cases are secured by snaps. Pull up the front of the upper case
first, as shown below.
Also, do not apply too much force when pulling it.
A
Figure 2-1. Top Case Removal
Keyboard and LCD PCBs
1. Disconnect the flat cable from the connector on the keyboard PCB.
2. Remove the keyboard PCB.
3. Disconnect the flat cable from the connector on the LCD PCB.
4. Remove the LCD PCB.
VV1I
1
e
C5
Figure 2-2. Keyboard and LCD PCBsRemoval
2-1

Main PCB
1. Remove the insulator board.
2. Remove 2 screws B securing the main PCB and bottom case.
3. Remove the main PCB.
B
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C)
CD
U
Figure 2-3. Main PCB Removal

III. MAINTENANCE
To Clean the Body and LCD Display
1. To avoid operational trouble, always keep the Tandy 102 clean.
2. Clean the body and the LCD screen using a soft, dry, lint-free cloth.
3. For tough stains, clean the body or the LCD screen with benzol.
Caution:Do not use any solvents other than benzol.

á

IV. THEORYOF OPERATION
General
Figure 4-1 shows how this section is organized and highlights significant areas.
Theory of
Operation
General Block
Diagram CPU I 1 Memory
Address
Decoding and
BankSelection
Circuit
Keyboard
System Bus
Cassette
Interface
Circuit
11
Read Circuit
Remote Circuit
Clock Control
Circuit
Timer Set
Sequence
Timer Read
Sequence
PrinterInterface
Circuit
Serial Interface
Circuit
Bar Code
Reader Interface
Circuit
LCD
fRS-232C/
LCD Common
MODEM Driver
Selection Circuit
RS-232C LCD Segment
Interface Circuit Driver
MODEM IC LCD Waveform
Transmission
Filter Circuit
Reception Filter
Circuit
MODEM
Transmitting
Level
Adjustment
yMODEM
Connector
Circuit
Figure 4-1. Organization of Section IV
I
1
I/O Map
Buzzer Control
Circuit
Signal from PB5
of PIO
Using PIO Times
Output
Power Supply
and Auto- Power
ON/OFF Circuit
DC/DC
Converter
Low Power
Detection Circuit
Reset Circuit
4-1

Block Diagram
The Tandy 102 has three principal LSIs.
• 8OC85A CPU
This is the Central Processing Unit which controls all functions.
• 81C55 PIO
This is the Parallel Input/Output interface controller which controls the printer interface,
keyboard, buzzer, clock and LCD interface.
• 6402 UART
This is the Universal Asynchronous Receiver Transmitter which controls the serial interface
(RS-232C or MODEM).
The input/output for a cassette recorder and the input of the BCR are controlled by CPU directly
through its SOD, SID and RST5.5terminals.
ROM and RAMs are connected to the system bus. ROM is available only for alternative selection
from Standard or Option.
CPU
8OC85 CASSETTE
INTERFACE
ROM
32KB
STANDARD
RAM
8KB
FKEYBOARD PCB
IKEYBOARD i
PIO PRINTER
81 C55 INTERFACE
RAM
8KB
RAM
8KB I
iLCD
CONTROL
I I
I RAM
8KB
OPTION
ROM
32KB
OPTION
LCD P
UART
6402
SYSTEM BUS
SOCKET
Figure 4-2. System Block Diagram
CLOCK
LCD yPD1990AC
RS-232C
INTERFACE