Texas Instruments 990 User Manual

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~ 945424-9701
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TABLE OF CONTENTS
Title
Page
SECTION I. THEORY OF OPERATION
General ............................................................ 1-1
System Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
Keyboard ......................................................... 1-1
Video Display Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2
CRT Monitor .................................................... 1-2
Power/Logic PWB ................................................. 1-2
VDT Controller ..................................................... 1-7
Interface Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9
VDT Controller/Computer Interface ....................................... 1-9
Single-Bit Operations .............................................. .1-10
Multiple-Bit Operations ............................................ .1-10
Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-10
Interface Timing .................................................. 1-11
Hardware Interface Signals .......................................... .1-12
Software Interface ................................................ .1-13
Keyboard-to-Power/Logic PWB Interface ................................... .1-19
Keyboard Data (KBDT, 1-8) .......................................... 1-19
Keyboard Data Strobe (KBSIN-) ....................................... 1-19
Repeat (REPEAT - ). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-19
Power/Logic PWB-to-VDT Controller Interface ............................... .1-19
Keyboard Data (TET, 1, 2, T) ......................................... 1-19
Terminal Ready (TRD, 1, 2, T) ....................................... .1-19
VDT Controller-to-Power/Logic PWB Interface ............................... .1-19
Video (CVID/Vl V and GND) .......... , .............................. 1-21
Beep Enable (BET, 1, 2, T) .......................................... .1-22
Modem Audio (MODIN) ............................................ .1-22
Power/Logic PWB-to-CRT Monitor Interface ................................ .1-22
Principles of Operation .................................................. 1-23
Keyboard ......................................................... 1-23
Contact ~1atrix ................................................... 1-23
Encocer .. , ..................................................... 1-23
Mode Keys and Mode Select Logic ..................................... .1-23
Power/Logic PWB .................................................. .1-24
Buff er Register ................................................... 1-39
UART Transmitter ............................................... .1-39
UART Receiver ................................................... 1-39
LED Display ..................................................... 1-39
Repeat Logic .................................................... 1-39
Difference Amplifier ............................................... 141
Dual-Gain Video Amplifier .......................................... .141
Ve:tr:-1.i Sync Generator ............................................ .142
I-l-Iinve Generator ................................................. 142
f\udiu ( i• cuitry ................................................... 144
CRT Monitor . . . . . . . . ........................................... .144
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Digital Systems Division

Texas Instruments 990 Specifications

General

Brand	Texas Instruments
Model	990
Category	Desktop
Language	English