Radio Shack TRS-80 User manual

TRS-80®
MICRO COLOR COMPUTER
MODEL MC-10
Catalog Number 26-3011
CUSTOM MANUFACTURED FOR RADIOSHACK, A DIVISION OF TANDY CORPORATION
26-3011

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TABLE OF CONTENTS
SECTION PAGE
NUMBER NUMBER
I SYSTEM DESCRIPTION - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3
II SPECIFICATIONS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 7
III DISASSEMBLY / REASSEMBLY - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 9
IV THEORY OF OPERATION - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 11
CPU-6803 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 12
Reset Circuit - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 12
ROM - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 12
Cassette Interface - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 12
Detailed Tape Format Information - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 13
RS-232C Interface - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 14
I/O Connector - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 15
Keyboard Interface - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 16
TV Switch Box - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 16
Power Supply - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 17
VDG - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 17
Device Selection - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 19
System Timing - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 19
RAM - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 20
Modulator - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 20
V TROUBLESHOOTING - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 21
VI PARTS LIST - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 25
VII PRINTED CIRCUIT BOARDS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 30
VIII IC INTERNAL CONNECTIONS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 33
IX SCHEMATlC DlAGRAM - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 44
X EXPLODED VlEW - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 46
[ Editor’s Note: I would also like to express my thanks to RadioShack for permit-
ting the distribution of this manual. I hope you find it useful. I have found a few
typos and inconsistencies in the Service Manual that I have noted in an italized
font like this. JMM.]

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SECTION I
SYSTEM DESCRIPTION

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SYSTEM DESCRIPTION
The MC-10 Micro Color Computer is a fully
expandable microprocessor system. It is com-
posed of a 6803 central processing unit, 4K of
static RAM, 8K of Basic ROM, and a 6847 video
display generator. The microcomputer is also
interfaced to a 48-key keyboard and provides
the logic to execute a 1500 Baud cassette inter-
face and a RS-232 serial interface. The system
operates on a common color burst frequency
of 3.579545 MHz. This main clock is divided by
4 in the CPU to yield an operating speed of 0.89
MHz.
In operation, the 4K of static RAM is shared
between the CPU and the video display gene-
rator. This time multiplexing is based on the
processor clock E. The CPU will be granted
access to the RAM (upon request) only during
the high state of E. This allows efficient usage
of the RAM with no waiting by the CPU and no
visible conflict on the display.
The 6847 VDG provides a display on a TV
screen of 32 characters by 16 rows. It also
allows a 64 x 32 semigraphics mode with eight
colors. This display utilizes a minimum amount
of system RAM (512 bytes).
The final elements of the microcomputer sys-
tem are the I/O devices. The MC-10 is interfaced
to a 48-key keyboard which generates the
codes for upper and lower case characters,
graphics symbols, and single stroke keyboard
entry. The computer also provides a 1500 baud
cassette interface for fast and reliable data and
program storage and a limited signal RS-232C
interface. The RS-232C interface allows either a
printer or a modem to be used with the MC-10.

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SYSTEM BLOCK DIAGRAM

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MEMORY MAP
Hex Address
C000 - FFFF 16K ROM (only 8K used)
9000 - BFFF 16K I/O Slot (Keyboard and VDG control)
4000 - 8FFF 16K RAM (4K - 20K used)
0100 - 3FFF Not Used
0080 - 00FF RAM internal to the 6803
0015 - 007F Not Used
0014 RAM Control Register
0013 Not Used
0012 Not Used
0011 Not Used
0010 Not Used
000F Port 3 Control and Status Register
000E Input Capture Register (low byte)
000D Input Capture Register (high byte)
000C Output Compare Register (low byte)
000B Output Compare Register (high byte)
000A Counter (low byte)
0009 Counter (high byte)
0008 Timer Control and Status Register
0007 Not Used
0006 Not Used
0005 Not Used
0004 Not Used
0003 Miscellaneous I/O Data Register
0002 Keyboard Output Lines
0001 Data Direction Register for miscellaneous I/O
0000 Data Direction Register for keyboard lines

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SECTION II
SPECIFICATIONS

– 8 –
SPECIFICATIONS
Power Supply
AC/AC adaptor Input 120V/60Hz
Output 8.0V/1.5A 16W
RF Modulator Ch. FC (MHz) Fsc (MHz)
For U.S.A./CANADA 3 61.25 +/-0.25 4.5 +/-0.2
4 67.65 4.5
Output Impedance 75 ohm
RF Output Terminal RCA jack
RF Output Level 1.5 - 2.8 mV at 75 ohm
Central Processing Unit
6803 8-bit processor
clock speed 0.89 MHz
Memory Size
ROM (for BASIC) 8K
RAM 4K (expandable up to
20K-external)
Video Display
Character display 512 (32 x 16) upper case
characters
Semi-Graphic display 64 x 32 elements
Color 8 colors - Green, Yellow,
Blue, Red, Buff, Cyan, Magenta, Orange
Interface
Printer RS232C, 4 pin DIN
Cassette 5-pin DIN 1500 baud
Bus line 34-pin Cartridge connector
Switch Box
Isolation more than 60 dB
Dimensions
8-1/2" x 1-7/8” x 7”
Weight
1.75 Ibs (.7875 kilograms)

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SECTION III
DISASSEMBLY / REASSEMBLY

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DISASSEMBLY
1. Unplug the units from the AC wall outlet
and disconnect all cables from the rear
panel.
2. Turn the computer over and remove the
four screws from the case bottom. One of
the screws is located under the warranty
seal in the upper right corner of the case
bottom.
3. Turn the computer right side up. Discon-
nect the snap locks located on the right and
left side of the case by placing a slotted
screw driver in the groove between the top
and bottom cases, approximately 2.7
inches from the rear of case. Push in and
turn the screwdriver to pop the case apart.
4. Disconnect Keyboard cable from wire con-
nector. NOTE: Pull flat wire upward.
5. Remove three screws that fasten the PC
Board to the bottom of the case. Remove
the PC Board.
6. Use tweezers to remove eleven clips that
fasten the bottom shield to the P.C. Board.
7. Locate the eight positions where the top
shield is soldered to the PC Board. Remove
this solder with solder wick or a desolder-
ing tool. Bend the protruding edge of the
shield upward until it is parallel to the slot
and remove top shield.
REASSEMBLY
1. Install the top PC Board shield. Solder the
shield to the ground plane at eight points.
2. Install the bottom shield with metal side up.
Secure to the PC Board with eleven clips.
3. Install PC Board in bottom of case. Secure
with three screws.
4. Install the two keyboard cables in their
respective connectors. This will be easier if
both hands are used and you are facing
rear of unit. Refasten cable restraints.
5. Join the top and bottom cases and push
them together at the snap lock positions.
This is a tight fit, therefore repositioning of
the cases may be required.
6. Install four screws in bottom of case.
1. Removal of Top Cabinet
Remove 4 screws as shown in Figure A.
Figure A
2. Removal of P.C. Board
Remove flat wires of keyboard from con-
nector.
Remove 3 screws as shown in Figure B.
Figure B
3. Removal of Keyboard
Remove 4 screws as shown in Figure C.
Figure C