26-3011 TRS-80® MICRO COLOR COMPUTER MODEL MC-10 Catalog Number 26-3011 CUSTOM MANUFACTURED FOR RADIO SHACK, A DIVISION OF TANDY CORPORATION
TABLE OF CONTENTS SECTION NUMBER PAGE NUMBER I SYSTEM DESCRIPTION - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3 II SPECIFICATIONS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 7 III DISASSEMBLY / REASSEMBLY - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 9 IV THEORY OF OPERATION - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - CPU-6803
SECTION I SYSTEM DESCRIPTION –3–
SYSTEM DESCRIPTION The MC-10 Micro Color Computer is a fully expandable microprocessor system. It is composed 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 interface and a RS-232 serial interface. The system operates on a common color burst frequency of 3.579545 MHz.
SYSTEM BLOCK DIAGRAM –5–
MEMORY MAP Hex Address C000 - FFFF 9000 - BFFF 4000 - 8FFF 0100 - 3FFF 0080 - 00FF 0015 - 007F 0014 0013 0012 0011 0010 000F 000E 000D 000C 000B 000A 0009 0008 0007 0006 0005 0004 0003 0002 0001 0000 16K ROM (only 8K used) 16K I/O Slot (Keyboard and VDG control) 16K RAM (4K - 20K used) Not Used RAM internal to the 6803 Not Used RAM Control Register Not Used Not Used Not Used Not Used Port 3 Control and Status Register Input Capture Register (low byte) Input Capture Register (high byte) Output Compare Regis
SECTION II SPECIFICATIONS –7–
SPECIFICATIONS Power Supply AC/AC adaptor RF Modulator For U.S.A./CANADA Output Impedance RF Output Terminal RF Output Level Input Output 120V/60Hz 8.0V/1.5A 16W Ch. 3 4 FC (MHz) 61.25 +/-0.25 67.65 Fsc (MHz) 4.5 +/-0.2 4.5 75 ohm RCA jack 1.5 - 2.8 mV at 75 ohm Central Processing Unit 6803 8-bit processor clock speed 0.
SECTION III DISASSEMBLY / REASSEMBLY –9–
DISASSEMBLY 1. Removal of Top Cabinet Remove 4 screws as shown in Figure A. 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.
SECTION IV THEORY OF OPERATION – 11 –
CPU-6803 RESET CIRCUIT The main component of this microcomputer system is the 6803 CPU. This is a 40-pin integrated circuit which provides the address, data, and miscellaneous control signals. The CPU receives the main clock frequency of 3.579545 MHz from the modulator assembly and divides this by 4 to produce an operating frequency of 0.89 MHz. This frequency is available as the processor clock E. The reset circuit is composed of switch S1 diode D9, resistor R24, capacitor C8, and two gates of IC U12.
tor equal to 1/2 volt. Since the other input is biased at 1 volt, the comparator output is switched to the high state. If the AC input from the recorder is positive, diode D6 is turned off and the input to the comparator will be at some point greater than 1 volt, in which case, the comparator output will be low. The input circuit is a zero crossing detector. R12 is a termination resistor for the cassette output. Resistors R16 and R17 are used to bias one input of the comparator at 1 volt.
RS-232C INTERFACE thus if the input voltage is greater than 2.6 volts, the comparator is turned on. The comparator outputs are open-collector so pull-up resistors R8 and R9 are required. The RS-232C interface utilizes a 4-pin DIN connector (J2). This interface allows the computer to have serial communication with printers, modem, or other computers. The four signals used by the interface are: 1. CD — a status input line 2. RS232lN — serial data input 3. GROUND — zero voltage reference 4.
I/O CONNECTOR external memory modules or ROM software modules. Table 1 provides a complete list of the signals and a brief description of each. In addition to serial interfaces, the MC-10 also provides a full complement of CPU bus signals that are accessible at the 34-pin cartridge connector. This allows expansion of the MC-10 with Table 1.
KEYBOARD INTERFACE To read the keyboard, only one column is enabled by writing a zero to one of the eight CPU I/O lines that corresponds to that column, and by writing ones to all the other lines. If a key has been pressed in that column, one of the input lines will be a zero and the key location will correspond to the bit that is low. By scanning each column in the keyboard, all of the keys may be checked.
POWER SUPPLY In the MC-10 the 4K of RAM is shared between the CPU and video display generator. This is accomplished by providing buffers between the address lines (U5 and U6) the data line (U7), and synchronizing the operation of the VDG to the CPU. The MC-10 power supply utilizes an external power pack to supply 8 VAC at 1.5 amps. This input AC voltage is connected through the power switch to the bridge rectifier.
Table 2.
DEVICE SELECTION allows an external device to change the MC-10 memory map. Also, the disable signal for the memory write is ORed with A12 to prevent a complete overlap of the 4K of RAM into the 16K memory map segment. A 74LS155 is used along with four OR gates and two inverters to provide device selection in the MC-10. The 74LS155 uses A15 and A14 to divide the memory map into four 16K segments. The bottom 16K segment is not used externally to the CPU. The next 16K segment is used for system RAM.
MODULATOR The MC6847 (VDG) has access to the RAM during the low portion of the E clock. Also during the low portion of E, the signal AS is used to latch the address lines in the latch (U2). During the high portion of E, all CPU address and data lines are valid and any accesses to the RAM or ROM occur during this time. The outputs from the MC6847 are connected directly to the modulator. The modulator unit is built around the MC1372.
SECTION V TROUBLESHOOTING – 21 –
TROUBLESHOOTING VIDEO INTERFACE Problems with the MC-10 may be separated into two major areas - I/O problems and dead computer problems. If the computer will display the sign-on message, then a fairly simple set of testing procedures may be used to isolate the problem. If, however, the computer displays random characters on the screen or has no display, then a major failure has occurred. Almost all of the work for the video interface is performed by the VDG (U11 - MC6847).
RS-232 INTERFACE ground. If this shows zero resistance, the problem is a short to ground. The RS-232 interface uses three simple level converter circuits. Isolating the problem will be an easy job of comparing the input to the output. If the +5 output is not shorted, check the voltage with the power pack plugged in. You should have 8 VAC at the power ON-OFF switch. If this looks good, check the input to the regulator. Here you should see a full wave rectified voltage of 10 volts DC.
ADJUSTMENT OF VSB (vestigial side band) FILTER CH. 4 Make Connection according to Figure 7 IC1 Luminance In 12 RF Out RCA JACK 0.01 5 ± 0.1V C116 L102 L103 L101 75Ω Coaxial Cable DC Power Supply SPECTRUM ANALYZER 75Ω COAXIAL CABLE INPUT TRACKING GENERATOR 2. 3. 4. 5. 6. 7. 50/75Ω Impedance Video Carrier Figure 7 Adjust marker of tracking generator at 61.25 MHz (marker - 2) Adjust L102 so lower side band peak point meets 61.25 MHz (marker - 2) Adjust marker of tracking generator at 72.
SECTION VI PARTS LIST – 25 –
PRINTED CIRCUIT BOARD PARTS CAPACITORS Ref.No. Value (µF) C1 C2 C3/4 C5 C6 C7 C8 C9~12 C13 C14~20 C21/22 C23 C24~26 C27 C28 C29 C30~32 C33 4700 10 100 0.1 0.0022 0.022 4.7 0.022 0.1 0.1 0.022 0.022 0.022 0.1 0.022 0.022 0.022 150P Voltage (V) Tolerance ( %) 16 25 16 25 50 50 50 50 25 50 50 16 50 25 50 16 50 50 ±20 ±20 ±20 ±20 +80/-20 +80/-20 ±20 +80/-20 ±20 ±5 +80/-20 ±30 ±80/-20 ±20 +80/-20 ±30 +80/-20 ±5 R/S Part No.
RESISTORS Ref.No. Value (ohms) R1 R2 R3 R4 R5 R6/7 R8/9 R10 R11 R12 R13 R14 R15/16 R17 R18 R19 R20 R21 R22/23 R24 R25 R26 100 3.9K 1.5K 10K 15K 10K 4.7K 75K 24K 220 8.2K 6.8K 56K 15K 1.5M 4.7K 10K x 8 4.7K 4.7K 100K 4.7K 100K Wattage 1/2 1/6 1/6 1/4 1/4 1/4 1/4 1/6 1/6 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/6 1/4 1/4 1/4 Tolerance ( %) ±5 ±5 ±5 ±5 ±5 ±5 ±5 ±5 ±5 ±5 ±5 ±5 ±5 ±5 ±5 ±5 ±5 ±5 ±5 ±5 ±5 ±5 R/S Part No.
Ref. No. U8 U9/10 U11 U12 U13 U14 U15 U16 U17 U18 U19 U20 Description R/S Part No. SN74LS174N or (D-TYPE F.
EXPLODED VIEW PARTS LIST Ref. No. 1 2 3 4 5 6 7 8 9 10 11 12 13 F1 F2 F3 F4 F5 Description R/S Part No. R/S Part No. Cabinet Ass’y, Top Cabinet, Top Plate, Model Cover, Connector Key Board Ass’y Knob, Reset (Red) Holder, SW Reset Case, Shield P.C. Board Ass’y Modulator, MDV-1 (Custom) Connector, Flat Wire Sheet, Shield Knob, Channel (Black) Cabinet, Bottom Foot, Rubber Screw, Top Tite 3x12 BT-B For Cabinet Screw, Top Tite 3x 8 BT-B For Key Board Screw, Top Tite 3x 8 PT-B For P.C.
SECTION VII PRINTED CIRCUIT BOARDS – 30 –
MAIN P.C.B.
(BOTTOM VIEW) – 32 –
SECTION VIII IC INTERNAL CONNECTIONS – 33 –
IC INTERNAL CONNECTIONS U1 MC6803G (Motorola) or HD6803P (Hitachi) – 34 –
U11 MC6847P (Motorola) – 35 –
U2 SN74LS373N (Motorola) or MB74LS373M (Fujitsu) U7 SN74LS245N (Motorola) or MB74LS245M (Fujitsu) – 36 –
U3 MB8364M (Fujitsu) U9/10 µPD4016C-1 (NEC) or µPD4016D-1 (NEC) or MB8128-15P (Fujitsu) or MSM2128-20RS (Oki) – 37 –
U4 SN74LS155N (Motorola) or MB74LS155M (Fujitsu) or HD74LS155P (Hitachi) U5/6 SN74LS367AN (Motorola) or MB74LS367AM (Fujitsu) or HD74LS367AP (Hitachi) – 38 –
U8 SN74LS174N (Motorola) or MB74LS174M (Fujitsu) or HD74LS174P (Hitachi) U14 MC14503BCP (Motorola) or HD14503BP (Hitachi) or µPD4503BC (NEC) or MSM4503RS (Oki) U19 SN74LS76AN (Motorola) or MB74LS76AM (Fujitsu) or HD74LS76P (Hitachi) – 39 –
U12 SN74LS14N (Motorola) or MB74LS14M (Fujitsu) or HD74LS14P (Hitachi) U13 SN74LS32N (Motorola) or MB74LS32M (Fujitsu) or HD74LS32P (Hitachi) U20 SN74LS32N (Motorola) or MB74LS32M (Fujitsu) or HD74LS32P (Hitachi) – 40 –
U15 LM339N (Motorola) or µPC339C (NEC) U18 SN74LS74AN (Motorola) or MB74LS74AM (Fujitsu) or HD74LS74AP (Hitachi) – 41 –
U16 MC1741CP1 (Motorola) or HA17741PS (Hitachi) U17 MC7805CT (Motorola) or NJM7805A (JRC) or µPC7805H (NEC) – 42 –
SECTION IX SCHEMATlC DlAGRAM SECTION X EXPLODED VlEW – 43 –
RADIO SHACK, A DIVISION OF TANDY CORPORATION U.S.A.: FORT WORTH, TEXAS 76102 CANADA: BARRIE. ONTARIO L4M 4W5 TANDY CORPORATION 6A3 AUSTRALIA BELGIUM U. K. 91 KURRAJONG ROAD PARC INDUSTRIEL DE NANINNE BILSTON ROAD WEONESBURY MOUNT ORUITT, N.S.W. 2770 5140 NANINNE WEST MIDLANDS WS10 7JN Printed in U.S.A.
