The Data General Nova 800 Minicomputer As a Digital Controller
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\ THE DATA GENERAL NOVA 800 MINICOMPUTER AS A DIGITAL CONTROLLER John William Pounds DUDLEY KNOX U8RARV NAVAL POtTQRADUATI SCHOOL MONTEREY, CALIFORNIA 93M0 Uit UATE onterey, California TH THE DATA GENERAL . NOVA 800 MINICOMPUTER AS A DIGITAL CONTROLLER by John William Pounds, Jr. September 1975 Thesis Advisor: Donald E. Kirk Approved for public release; distribution unlimited. T169787 Unclassified i'llCIJHITY CL AS5I FIC * TION OF THIS P »GEfH hnn Drla fnljr.' 20. A system operation tutorial is offered which includes a programmed instruc tion section to efficiently familiarize the prospective user. Finally, examples of system use as a digital controller are provided. DD 1473 lj2™3 Unclassified S/N 0102-014-G601 SECURITY CLASSIFICATION OF THIS P*GEf»Ti«n D»l» Enffd) 2 The Data General Nova 800 Minicomputer As a Digital Controller by John William Pounds, Jr. Lieutenant, United States Navy B.S.E.E., University of New Mexico, 1970 Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN ELECTRICAL ENGINEERING from the NAVAL POSTGRADUATE SCHOOL September 1975 c/ DUDLEY KNOX LIBRARY NAVAL POSTGRADUATE SCHOOL TEREY. CALIFORNIA 93940 ABSTRACT The Data General Nova 800 minicomputer is described in detail. An analysis is made of its instruction set and a description is given of available peripheral equipment. The specification criteria for A/D and D/A devices is discussed and the selection of specific devices is supported. The DT 1620 data acquisition system and the DT 212 D/A converter are described. The interface considerations for adapting the A/D and D/A converters to the Nova system are discussed. Programming examples for the combined system are given. A system operation tutorial is offered which includes a programmed instruction section to efficiently familiarize the prospective user. Finally, examples of system use as a digital controller are provided. TABLE OF CONTENTS I. INTRODUCTION 10 A. PROBLEM STATEMENT 11 II. THE NOVA 800 COMPUTER 13 A. INTRODUCTION 13 B. THE INSTRUCTION SET __ 15 1. Memory Reference Instructions 16 2. Arithmetic and Logical Instructions 18 3. I/O Instructions 21 4. Mnemonics 23 C. THE DATA CHANNEL 24 D. SPECIAL OPTIONS 25 E. THE OPERATING SYSTEM 26 1. Self-Loading Bootstrap and Image Core Loader /Writer 26 2. Command Line Interpreter 28 3 . Text Editor 31 4. Assembler 34 5. Relocatable Loader 38 F. GENERAL PROGRAMMING 41 III. DATA ACQUISITION AND DISTRIBUTION 47 A. INTRODUCTION 47 B. RESOLUTION AND SPEED COSTS 47 C. THE INTERNAL ANALOG PERIPHERAL 49 D. GENERAL INTERFACE EQUIPMENT 51 E. THE DT 1620 56 1. Multiplexer and Differential Amplifier 58 2. Sample and Hold Circuit 61 3. 12_bit A/D Converter 61 4. Special Options 62 F. THE DT 212 63 G. INTERFACE CONSIDERATIONS 64 1. Device Selection 64 2. Control Signals 65 3. Setting the DONE Flipflop 68 H. CALIBRATION OF THE A/D AND D/A CONVERTERS 70 I. SYSTEM PROGRAMMING 71 IV. SYSTEM OPERATION TUTORIAL 79 A. INTRODUCTION 79 B. MACHINE OPERATION 79 C. SYSTEM FAMILIARIZATION 83 V. EXAMPLE CONTROL PROBLEMS 88 A. INTRODUCTION 88 B. PROGRAM DEVELOPMENT 89 C. MINIMUM PROTOTYPE DESIGN 95 D. RIPPLE FREE RESPONSE 97 VI. CONCLUSION 102 A. EVALUATION OF THE NOVA COMPUTER 102 B. EVALUATION OF THE A/D EQUIPMENT 103 C. EVALUATION OF THE D/A EQUIPMENT 103 D. EVALUATION OF THE SYSTEM 103 E. RECOMMENDATIONS FOR EXPANSION 104 APPENDIX A Instruction Mnemonics 105 APPENDIX B Basic A/D and D/A Conversion 116 B. 1 Basic D/A Conversion 118 B. 2 Successive Approximation A/D Conversion System 120 B. 3 Counter Ramp A/D Conversion 120 B.4 Parallel A/D Conversion 122 APPENDIX C Bus Signals 124 APPENDIX D Device Connection and Specification 129 D. 1 Device Connection 129 D. 2 DT 1620 Functional Pin Description 132 APPENDIX E Assembler Error Flags 142 APPENDIX F Manufacturer Supplied Subroutines 144 APPENDIX G Instruction Execution Times 152 BIBLIOGRAPHY 154 INITIAL DISTRIBUTION LIST 155 LIST OF FIGURES Figure 1. 1 Basic Interface Elements 10 2. 1 Memory Reference Instruction Formats 16 2.2 Arithmetic and Logic Instruction Formats 18 2. 3 Organization of Arithmetic Unit 20 2.4 I/O Instruction Format 21 3.1 Relative Cost vs Resolution 48 3.2 Data Bus Control Circuit 52 3.3 Control Signal Inverters 53 3.4 Device Select Circuit 54 3.5 Done and Busy Flipflop Control 55 3.6 DT 1620 Simplified Schematic 57 3.7 Common Mode Voltage Model 58 3.8 Single- Ended Input Mux 59 3. 9 Differential Input Mux 60 3. 10 DT 1620 Output Coding 62 3. 11 DT 212 Simplified Schematic 63 3. 12 Device Select Separation 65 3. 13 Relative Timing Diagram for Programmed Transfers 68 5. 1 Example Control System 88 5.2 Comparison of Continuous and Sampled Systems 99 5.3 Minimum Prototype Response 100 5.4 Minimum Ripple Response 101 B-l Example Digital Coding 116 B-2 Digital Word vs Equivalent Analog Voltage 117 B-3 Basic D/A Conversion 119 B-4 Successive Approximation A/D Converter 121 B-5 Counter Ramp A/D Converter 122 B_6 Parallel A/D Conversion 123 I. INTRODUCTION During the past decade, the use of the digital computer in complex control systems has increased at an extraordinary rate. System designs incorporating the use of a digital machine have become common, place in industry as well as the military. These sample-data systems are being designed and interfaced to existing systems to improve reli- ability, speed of response, and accuracy. Even though the individual systems differ in complexity the basic configurations are the same. The basic elements of any interface between a digital processor and an analog system are shown in Figure 1. 1. Continuous Discrete Discrete Discrete Analog Digital Digital Analog Analog- To- Digital Digital- To -Ana log \ Computer / Converter Converter Figure 1. 1 Basic Interface Elements The analog-to-digital converter samples the continuous signal on com- mand by the computer. It then converts the voltage sampled into a digital word of the form used by the computer. The computer performs some specified operations on the word and feeds the resulting digital output to the digital-to-analog converter. The digital-to-analog con- verter transforms the digital word into a discrete analog pulse. 10 One point of contention between system designers has been whether to design a special purpose computer for a given task or to use a general purpose computer which may be used in a variety of tasks. This deci- sion is dependent upon the problem to be solved. For the special pur- pose computer, the advantages are smaller size, less cost and ease of interface design. For the general purpose computer, the major advan- tage is flexibility through multiprocessing. In recent years, the size of general purpose computers has dimin- ished with the emergence of the minicomputer. Large core memories have given way to the use of electronic memories using Large Scale Integration (LSI). And the large magnetic tape reel-to- reel units have been replaced by cassette tape storage. The minicomputer and its associated mini-peripherals are in general slower, less powerful, and less sophisticated than the large general purpose machines, but have the advantages of smaller size, lower cost, and simplicity while still having a great deal of flexibility. Recently, through additional mini- aturization, the interface elements have become small enough so that they may be placed inside a minicomputer chassis on an interface board. This thesis is concerned with the incorporation of such an ADC- DAC system with the Data General Nova 800 computer. A. PROBLEM STATEMENT In 1974, the Electrical Engineering Department of the Naval Post- graduate School purchased a Data General Nova 800 computer for use in 11 C the area of automatic control. The computer was not equipped with A/D or D/A devices but it was felt that an interface could be designed and built to provide these functions and thereby make it possible to use the system as a digital controller. The problem was not only to inter- face the hardware but also to provide a basic manual for machine operation, give a description of the operational computer system, and supplement the references in the area of programming. Chapter 2 describes the Nova computer and the associated peripherals. It includes a complete analysis of the instruction set, describes the software of the operating system, and introduces the general elements of programming. The computer description pre- supposes a familiarity with general minicomputer organization and operation. Chapter 3 provides the specification criteria for the A;' and D/A converters, supports the selection of specific de%r ices, des- cribes the interface board available with the computer, gives the inter- face design considerations, and introduces software programming v.uth reference to A/D and D/A devices. Chapter 4 is a system tutorial. "_-. •:.'. -. - . -. .-. : . -•--:•....:._ : . : :\ :\ : -: y : ' : r :u.„ ; a ; : c i s e : :ur.a: fcr cui ref- erence and a step-by-step procedure for Learning the elements of computer operatic." cue programming. Charter 5 provides examples of the use of the svstcm as a uuui controller fcr a simulated continuous plant. Chapter v cives ar. evaluation of the sy stent elements and zi ::. svste: ~ a whole and recommends directions fcr expansion. 12 ^ II. THE NOVA 800 COMPUTER A. INTRODUCTION The Nova 800 is a general purpose, 16-bit word length computer. It is organized around four accumulators, ACO - AC3. Both AC2 and AC3 can also be used as index registers. The mainframe is 10 inches high and mounts inside a standard 19-inch chasssis. It has 17 slots; two are used for the central processor leaving 15 available for memory and 1/0 interfaces.