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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MEMORY MAP
The first page of the Memory Map (page 5) shows the break-
down of the large blocks of memory in the Color Computer.
One variable in this block is the video display which may be
located anywhere in the memory. BASIC normally locates the
video display at the Hexidecimal addresses 0400 -05FF.
The next two pages of the Map explain the addressing for the
PIA's. In general, the even numbered memory locations are the
I/O registers and the odd numbered memory locations are the
controll registers. Bit two of the control registers determines
what is addressed at the even numbered memory locations. If
this bit is set high (logic 1) the data I/O register is addressed.
If it is set low the data direction register is addressed. Norm-
ally the data direction register is addressed only during initial-
ization to allow configuration of the data inputs and outputs.
(By clearing bit 2and writing to the even numbered memory
location one address below, each bit of the PIA may be set as
an input or an output. A1in the data direction register sets
the bit as an output and asets the bit as an input.)
The addresses from FFC0-FFDF are the control registers for
the SAM address multiplexer chip. There are no data lines to
the SAM chip therefore two addresses are used to control each
register. In general, writing any data to an even numbered
memory location will clear the register and writing any data to
an odd numbered memory location will set the register. Ad-
dresses FFC0-FFC5 control the display mode. To select a cer-
tain display mode, both these registers and the PIA controlling
the VDG chip must be set to the proper mode. However,
it is also possible to set the SAM registers to one mode and the
PIA controlling the VDG to another mode, and obtain a
useful video mode. These cross modes are explained in more
detail in the Video Interface section.
Addresses FFC6-FFD3 control the display starting address. If
all of the registers are cleared, the display will begin at 0000.
Normally register F2 will be set causing the display to start at
0400. This feature of the SAM chip allows the display to be
paged through all of the RAM. Register P1 controls afeature
which is not used in the Color Computer. Therefore, it should
be cleared at all times.
Addresses FFD6-FFD9 control the clock speed of the CPU.
The Color Computer is designed to operate at 0.89 MHz.
Addresses FFDA-FFDD control the memory size set up of the
SAM chip. These addresses select 4K, 16K, or 32K of RAM in
the Color Computer. This memory size option should be
changed only by the reset routine in BASIC. Changes at other
times may erase the contents of RAM. Register TY, at ad-
dresses FFDE -FFDF, should be cleared at all times.
The final series of addresses in the Color Computer are the
interrupt and reset vectors. Whenever the CPU receives areset
or interrupt it will load the address at the indicated location
and begin execution at the new location. The dual set of
addresses are listed because the vectors are mapped into the
top of the BASIC ROM (BFF2-BFFF), i.e., if the CPU reads
FFFF it will actually read the contents of BFFF.
However, it is also possible to set the SAM registers to one
mode and the PIA controlling the VDG to another mode, and
obtain auseful video mode. These cross modes will be
discussed in more detail in the Video Interface section.
4

COLOR COMPUTER MEMORY MAP
FF00
C000
A000
4000
3000
2000
1000
0000
n
CARTRIDGE
ROM
t\
BASIC
ROM
EXPANSION
ROM
A
4K RAM
A
16K RAM
32 KRAM
0600 ANORMAL VIDEO
0400 TDISPLAY
HEX
ADDRESS COLOR COMPUTER
USAGE

COLOR COMPUTER MEMORY MAP (cont'd)
FF00-FF03 PIA U8
BIT =KEYBOARD ROW 1and right joystick switch
BIT 1=KEYBOARD ROW 2and left joystick switch
BIT 2= KEYBOARD ROW 3
FF00 |BIT 3= KEYBOARD ROW 4
BIT 4= KEYBOARD ROW 5
BIT 5= KEYBOARD ROW 6
BIT 6= KEYBOARD ROW 7
BIT 7=JOYSTICK COMPARISON INPUT
Aura t,/0=1 RQ* to CPU Disabled
Control of the Horizontal 1= |RQ* to CPU Enabled
BIT1 sync clock (63.5 microseconds) ^Fl^glet on the falling edge of HS
Interrupt Input (1=Rag $et Qn the rjsing edge of HS
BIT 2=Normally 1:0=Changes FF00 to the data direction register
BIT 3=SEL 1:LSB of the two analog MUX select lines
FF01 {BIT 4= 1Always
BIT 5=1Always
BIT 6Not Used
BIT 7=Horizontal sync interrupt flag
BIT 0= KEYBOARD COLUMN 1
BIT 1= KEYBOARD COLUMN 2
BIT 2= KEYBOARD COLUMN 3
FF02 IB,T 3= KEYBOARD COLUMN 4
BIT 4= KEYBOARD COLUMN 5
BIT 5= KEYBOARD COLUMN 6
BIT 6= KEYBOARD COLUMN 7
BIT 7= KEYBOARD COLUMN 8
''BIT©
BIT 1
0=IRQ*toCPU Disabled
Control of the field sync clock \-|=|RQ*toCPU Enabled
16.667 Ms Interrupt Input j0= sets flag on falling edge FS
1= sets flag on rising edge FS
FF03 IBIT 2=NORMALLY 1:0= changes FF02 to the data direction register
BIT 3=SEL 2: MSB of the two analog MUX select lines
BIT 4=1Always
BIT5 =1Always
BIT 6Not Used
.BIT 7=Field sync interrupt flag

COLOR COMPUTER MEMORY MAP (Cont'd)
FF20-FF23 PIA U4
FF20
BIT =CASSETTE DATA INPUT
BIT 1=RS-232 DATA OUTPUT
BIT2 =6BITD/ALSB
BIT3=6BITD/A
BIT4 =6BITD/A
BIT5=6BITD/A
BIT6=6BITD/A
BIT 7=6BIT D/A MSB
FF21
BIT0
BIT1
Control of the CD
RS-232 status Input
1
FIRQ* to CPU Disabled
-FIRQ* to CPU Enabled
=set flag on falling edge CD
1=set flag on rising edge CD
BIT 2=Normally 1:=changes FF20to the data direction register
BIT 3=Cassette Motor Control :=OFF 1=ON
BIT 4=1Always
BIT 5=1Always
BIT 6Not Used
.BIT 7=CD Interrupt Flag
FF22
FF23
BIT =RS-232 DATA INPUT
BIT 1=SINGLE BIT SOUND OUTPUT
BIT 2= RAM SIZE INPUT LOW =4K
BIT 3=VDG CONTROL OUTPUT
BIT 4=VDG CONTROL OUTPUT
BIT 5=VDG CONTROL OUTPUT
BIT 6=VDG CONTROL OUTPUT
BIT 7=VDG CONTROL OUTPUT
BIT0 I
1Control of the Cartridge
BIT 1JInterrupt Input j=sets f,ag on faMing edge CART«
1=sets flag on rising edge CART*
BIT 2=Normally 1: =changes FF22 to the data direction register
BIT 3=Six BIT Sound Enable
BIT 4=1Always
BIT 5=1 Always
BIT 6=Not Used
BIT 7=Cartridge Interrupt Flag
HIGH =16K
CSS
GM0& INT/EXT
GM1
GM2
A/G
0= FIRQ*toCPU Disabled
1=FIRQ*toCPU Enabled
FF40- FFBF NOT USED

COLOR COMPUTER MEMORY MAP (Cont'd)
FFDF
FFDE
FFDD
FFDC
FFDB
FFDA
FFD9
FFD8
FFD7
FFD6
FFD5
FFD4
FFD3
FFD2
FFD1
FFD0
FFCF
FFCE
FFCD
FFCC
FFCB
FFCA
FFC9
FFC8
FFC7
FFC6
FFC5
FFC4
FFC3
FFC2
FFC1
FFC0
TY MAP
TYPE
M0
1EMORY
SIZE
R1
R0
CPU
RATE
P1 PAGE #1
F6
F5
F4
F3
F2
F1
F0
DISPLAY
OFFSET
(BINARY)
V2
V1
V0
DISPLAY
MODE
CONTROL
(=0)
-N.U.
32/64K \
16K (Dynamic RAMs
,_4K '
-N.U.
_N.ll.
r- 0.9/1 .8 MHz ),.
{. Transparent
0.9 MHz only \Refresh
(=0)
Address of Upper- Left-Most
Display Element =0000 +(%K Offset)
N.U.—i
G6R,G6C
G3R
-G3C
G2R
G2CG1C,G1R
AI,AE,S4, S6
r

COLOR COMPUTER MEMORY MAP (Cont'd)
FFFFOR BFFF RESET VECTOR LSB
FFFEORBFFE RESET VECTOR MSB
FFFDOR BFFD NMI VECTOR LSB
FFFCORBFFC NMI VECTOR MSB
FFFBORBFFB SWI1 VECTOR LSB
FFFAOR BFFA SWI1 VECTOR MSB
FFF9 0R BFF9 IRQ VECTOR LSB
FFF8 0RBFF8 IRQ VECTOR MSB
FFF7 0RBFF7 FIRQ VECTOR LSB
FFF6 0R BFF6 FIRQ VECTOR MSB
FFF5 0R BFF5 SWI2 VECTOR LSB
FFF4 0R BFF4 SWI2 VECTOR MSB
FFF3 0RBFF3 SWI3 VECTOR LSB
FFF2 0R BFF2 SWI3 VECTOR MSB
FFF1 -FFE0 NOT USED

SECTION II
DISASSEMBLY/ASSEMBLY
11

DISASSEMBLY REASSEMBLY
1. Make sure all cables (also power cord) are disconnected.
Place the Color Computer face down on apadded or non-
scratching surface and remove the seven screws from the
Case Bottom. (Because the screws are positioned so
deeply, you may not be able to actually remove them
until the Computer is turned face up.)
2. Carefully place the Computer face up and lift off the Case
Top and set it aside.
3. Carefully lift the Keyboard off the plastic bosses and
remove the Keyboard Cable.
4. Remove the Top Cover Shield and set it aside. You may
have to remove the top cover of the modulator (U5) to
get the shield off.
5. Remove the three screws supporting the transformer
assembly (two on transformer, one on the board) and
disconnect all jumper cables.
6. Remove the ten screws fastening the CPU PC Board and
lift the Board off its plastic bosses.
7. Remove the Ground Plane and Insulator from the back of
the PC Board by using ascrewdriver or other small, thin
tool to pry off all sixteen fasteners from the rear of the
Board.
1. Replace the Ground Plane and its Insulator on back of
the PC Board and install the sixteen fasteners. You may
need some pliers to close the tips together and then insert.
2. Replace the PC Board onto the plastic bosses. Be sure that
the ends of the Power Cord are pulled through the square
cutout in the Board where the transformer is positioned.
3. Fasten the PC Board in place using ten #6 x1/2" screws.
4. Connect the transformer jumper cables, E1 through E4
and the Power Cord jumpers, E6 •white, E5 -green, and
E7 -black.
5. Position the Transformer assembly and attach jumper
cable E8. Fasten using two #6 x11/2" screws (on trans-
former) and one #6 x1/2" screw (on board).
6. Replace the Top Cover Shield.
7. Reconnect the Keyboard Cable and Cable Shield if used.
Replace the Keyboard onto the plastic bosses in the case
bottom.
8. Replace the Case Top onto the Case Bottom and carefully
turn the entire unit over (face down).
9. Replace the seven screws in the Case Bottom (two #6 x
7/8" toward the front and five #6 x11/4" toward the
rear). Do not put the longer screws in the front positions,
it could dent the Computer Case Top.
12

Transformer Assembly
CPU PC Board
Power Cord Assembly
Case Top
Top Covsr Shield
Keyboard
Ground Plane Insulator
Case Bottom
FIGURE 1. DISASSEMBLY/REASSEMBLY
13