Radio Shack TRS-80 Model 4 Technical Reference Manual

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TABLE OF CONTENTS
Part 1 / Hardware
SECTION I Introduction.....................................................................................................................................1
1.1 SYSTEM OVERVIEW ......................................................................................................................3
1.2 BLOCK DIAGRAM............................................................................................................................3
1.3 JUMPER OPTIONS..........................................................................................................................5
SECTION II Disassembly / Assembly................................................................................................................7
2.1 Disassembly .....................................................................................................................................9
2.1.1 Case .................................................................................................................................................9
2.1.2 CPU Board........................................................................................................................................9
2.1.3 FDC Board (optional)........................................................................................................................9
2.1.4 RS-232 Board (optional)...................................................................................................................9
2.1.5 Main Power Supplies........................................................................................................................9
2.1.6 Disk Drives (optional)........................................................................................................................9
2.1.7 Video Monitor (CRT) and Video Board...........................................................................................10
2.2 Assembly ........................................................................................................................................11
2.2.1 RS-232 Board (optional).................................................................................................................11
2.2.2 FDC Board (optional)......................................................................................................................11
2.2.3 CPU Board......................................................................................................................................11
2.2.4 Power Supply..................................................................................................................................11
2.2.5 Disk Drive (optional) .......................................................................................................................11
2.2.6 Disk Drive Power Supply (optional)................................................................................................11
2.2.7 Video Monitor (CRT) and Video Board...........................................................................................11
2.2.8 Case ...............................................................................................................................................11
SECTION III CPU Circuit Board ........................................................................................................................13
3.1 Model 4 Theory of Operation..........................................................................................................15
3.1.1 Introduction.....................................................................................................................................15
3.1.2 CPU and Timing .............................................................................................................................15
3.1.3 Buffering .........................................................................................................................................15
3.1.4 Address Decoding ..........................................................................................................................15
3.1.5 ROM ...............................................................................................................................................19
3.1.6 RAM................................................................................................................................................19
3.1.7 Keyboard ........................................................................................................................................19
3.1.8 Video...............................................................................................................................................19
3.1.9 Real Time Clock .............................................................................................................................21
3.1.10 Cassette Circuitry ...........................................................................................................................21
3.1.11 Printer Circuitry...............................................................................................................................21
3.1.12 I/O Connectors................................................................................................................................21
3.1.13 Sound Option..................................................................................................................................21
3.2 Model 4 I/O Bus..............................................................................................................................26
3.3 Model 4 Port Bits ............................................................................................................................28
Schematic 8000173, 64K Version CPU PCB 8858090..................................................................31
CPU Component Layout.................................................................................................................43
Parts List, CPU PCB #6700104AA3...............................................................................................45
Parts List, CPU PCB 8858090........................................................................................................49
SECTION IV Floppy Disk Interface ...................................................................................................................53
4.1 Model 4 FDC PCB #8858060.........................................................................................................55
4.1.1 Control and Data Buffering.............................................................................................................55

Radio Shack TRS-80 Model 4 Specifications

General

Brand	Radio Shack
Model	TRS-80 Model 4
Category	Desktop
Language	English