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                                       PREFACE




                                INTENDED AUDIENCE

The DOS-73 Technical Reference is written for technicians doing component-level
trou bleshooting of the DOS-73 Coprocessor board.



                         ORGANIZATION OF THIS MANUAL

System Features and Functions

              Briefly describes the physical features and functional capabilities of the
              DOS-73 Coprocessor board.

DOS-73: Theory Of Operation

              Describes the DOS-73 hardware and the functions performed by it.

Diagnostics

              Describes DOS-73 Coprocessor diagnostic procedures.




                                                                                      1.
                                                                                 CONTENTS



1:            System Features and Functions

General Description.................................................................................................................................                    1-2
DOS-7 3 Archi tecture................................................................................................................................                   1-2
DOS-73 Block Diagram...........................................................................................................................                         1-3



2:            DOS-73: Theory Of Operation

cPu..................................................................................................................................................................   2-2
Memory Organization..............................................................................................................................                       2-3
COM2: Emula tion......................................................................................................................................                  2-4
Timer Emulation........................................................................................................................................                 2-5
Interrupt System.........................................................................................................................................               2-5
I/O Intercept System................................................................................................................................                    2-6
Video Intercept System...........................................................................................................................                       2-7
Math Coprocessor Emulation...............................................................................................................                               2-7
UNIX Interface..........................................................................................................................................                2-8
Software Driver Specifications..........................................................................................................                                2-10
       DOS-73 Hard ware.......................................................................................................................                          2-10
       User Level Interface.................................................................................................................                            2-13



3:             Diagnostics

Testing The COM2: Port.........................................................................................................................                         3-2
Number Of Test Passes...........................................................................................................................                        3-2
Test Descriptions.......................................................................................................................................                3-3
In Case Of Trouble...................................................................................................................................                   3-6




11.
                                          1:     SYSTEM FEATURES AND FUNCTIONS




General Description.................................................................................................................................   1-2
DOS-73 Architecture................................................................................................................................    1-2
DOS-73 Block Diagram...........................................................................................................................        1-3




                                                                                                                                                             1-1
                         SYSTEM FEATURES AND FUNCTIONS




                                GENERAL DESCRIPTION

The DOS-73 coprocessor is a peripheral product designed to bring MS-DOS capabilities to
the AT&T UNIX PC. The DOS-73 hardware is essentially a PC "on a board," with several
enhancements. The hardware enhancements include: Hercules monochrome graphics emula-
tion (first page only), PC COM2: port emulation, Microsoft Mouse emulation using the
mouse, and increased performance due to a full 16 bit bus and increased clock speed. This
document describes the DOS-73 hardware and outlines the DOS-73/7300/UNIX interface
standards as ALLOY has defined them.



DOS-73 Architecture

The DOS-73 hardware was designed to parallel the PC architecture. The hardware also in-
cludes enhancements which allow it to be integrated into a multi-processor environment,
and improvements. The system includes the following:

              8086 CPU

              512K Bytes Dynamic RAM

              Memory Timing & Control Circuitry

              INS8250 Asynchronous Communications Element

              Interface Circuitry to the 7300 bus

              18259 Programmable Interrupt Controller

              18253 Programmable Timer

              V ideo Data Handling Circuitry

              I/O Intercept Circuitry

              8087 Numeric Coprocessor Hooks


A block diagram of the board is found on the following page.



1-2
System Features and Functions




DOS-73 BLOCK DIAGRAM

              I    COM2:        1

              ~                                                                             ~~;!3"r                       Refresh


              I~~~IM I                                           II                         r
              I                  ~
                  CM

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