View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Lehigh University: Lehigh Preserve Lehigh University Lehigh Preserve Theses and Dissertations 1-1-1979 A video display - graphics terminal for use with an S-100 based microcomputer. Thomas L. Carpenter Follow this and additional works at: http://preserve.lehigh.edu/etd Part of the Electrical and Computer Engineering Commons Recommended Citation Carpenter, Thomas L., "A video display - graphics terminal for use with an S-100 based microcomputer." (1979). Theses and Dissertations. Paper 2062. This Thesis is brought to you for free and open access by Lehigh Preserve. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of Lehigh Preserve. For more information, please contact [email protected]. A VIDEO DISPLAY - GRAPHICS TERMINAL FOR USE WITH AN S-100 BASED MICROCOMPUTEh by Thomas L. Carpenter, III A Thesis Presented to the Graduate Committee of Lehigh University in Candidacy for the Degree of Master of Science in Electrical Engineering Lehigh University 1979 ProQuest Number: EP76335 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest EP76335 Published by ProQuest LLC (2015). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 This thesis is accepted and approved in partial fulfillment of the requirements for the degree of Master of Science. -fer^ ?fofessor in Charge Chairman of DepartraenF -ii- ACKNOWLEDGEMENTS I wish to express ray appreciation to Professor A. I. Larky who was the major advisor for this thesis. I further wish to acknowledge the total support of my family during all phases of this project. My wife Carol, my daughter Becky, and my son Timothy, all relinquished a great deal of time so that 1 could devote my full attention to this thesis. -iii- CONTENTS PAGE Abstract 1 Introduction 3 Chapter 1 Functional Description ft Chapter 2 Custom Devices 11 Chapter 3 The Mode and Attribute Control 1*1 Chapter 4 The Character Formats 17 Chapter 5 The Address Bus ; 19 Chapter 6 The Data Bus 21 Chapter 7 Clocks and Character Timing 23 Chapter 8 Special Attributes and Other Funnies 25 Conclusions 27 iv TABLES PAGE Table 1: The CRT 5027 Capabilities 28 Table 2: The CRT 8002 Capabilities 29 FIGURES PAGE Figure 1 Block Diagram of Overall System 30 Figure 2: Division of Memory Sections 31 Figure 3: Screen Format 32 Figure 4 Character Block Format 33 Figure 5 Wide Graphics Character Format 34 Figure 6 Thin Graphics Character Format 35 Figure 7 Clocks and Attribute Latch 36 Figure 8: CRT in Alphanumeric Mode 37 Figure 9 CRT in Dot Graphics Mode 38 Figure 10: CRT in Mixed Mode 39 Figure 11 Block Diagram of Address Bus 40 Figure 12: Block Diagram of Data Bus 41 Figure 13: Timing Diagram 42 vi APPENDIX SYSTEM SCHEMATICS PAGE THE ADDRESS BUS 45 THE DATA BUS 46 CRT CONTROL CIRCUITRY 47 CLOCKS AND MODE CONTROL 48 1K MEMORY SECTION 49 VDGT CIRCUIT BOARD LAYOUT 50 vii ABSTRACT This paper describes a Video Display/Graphics Terminal(VDGT)- a system for intermixing alphanuraerics and dot graphics on a single TV monitor. The VDGT board plugs directly into an S-100 Bus Microcomputer and occupies 8K bytes of memory space divided into two separate memory sections - a IK byte section for stor- ing the alphanumeric characters and a 7K bytes section for storing a 256 X 22H dot matrix. Custom devices are incorporated into the VDGT to provide the synchronization signals, to generate the DMA addresses, and to convert the data into characters for display. These devices also provide the VDGT with four modes of operation and such attributes as Under- line, Reverse Video, Character Blank, etc. The four modes are the Alphanumeric mode, the Wide Graphic mode, the External Data (dot matrix) mode, and the Thin Graphics mode. This thesis describes an augmentation of these modes, Mixed Mode, which is the major distinguishing feature between this system and other hobby systems. This Mixed Mode allows all of the modes and attributes -1- to be intermixed on a character-by-character basis. This Mixed Mode includes displaying all or any portion of the 256 X 22*4 dot matrix intermixed with the other modes. The VDGT was constructed and interfaced to a SOL-20 microcomputer (which uses an Intel 8080 CPU and is organized around an S-100 bus). The detailed description of the system design and implementation is the basis for this thesis. -2- INTRODUCTION The introduction of the ALTAIR 8800 microcomputer in Popular Electronics in 1975 [1.2], can be credited with creating the home computing market. This system, comprised of an Intel 8080 microprocessor; a front panel with toggle switches and light emitting diodes; a memory board with 256 bytes of read/write random access memory (RAM); a power supply; and a cabinet; offered an easily expandable computer system at a price, an order of magni- tude, lower than commercial systems. It soon became ap- parent to many Altair owners that the human interface to such a powerful machine should consist of more than rea lights and toggle switches; furthermore, input/output dev- ices operating at Teletype speeds (10 characters per second) were not well matched to the CPU speed of 2 MHz. The DECWRITER terminal, with a speed of 30 characters per second, is neither fast enough nor inexpensive enough for the hobby market. Another new device also emerging at this tine was the Video-Keyboard Terminal (VKT). The VKT, which can accept input at rates up to 9600 baud and display its output on a Cathode Ray Tube (CRT), was adopted rapidly in the -3- minicomputer world by such manufacturers as Hewelett- Packard, Tektronix and Honeywell; but it too had the disadvantage of having a price comparable to that of the microcomputer itself. Nevertheless, the VKT stirred many to consider what minimum circuitry was necessary to implement its functions [3]. The CRT was, in many cases, an ordinary TV monitor built into the same cabinet as the keyboard; with elec- tronics to decode the keys and send the data to a local memory where it would be converted into the dot patterns needed to display the character. A video mixing circuit would combine the video synchronization information with the dot patterns and send the composite signal to the TV monitor. It was not long before the microcomputer enthusiasts published designs showing how to implement the VKT with an ordinary home TV set used for the monitor. These designs usually placed the character memory in the processor's address space and eliminated the need to send the data to a separate device. This allowed writing characters on the TV screen as fast as the program could read them and store them into memory. A full screen of 1024 characters could be updated in only 6 milliseconds! BYTE Magazine and others published articles [4,53 -4- showing the necessary circuitry needed to construct a TV Typewriter (VKT). Small companies started offering hardware to interface directly to the ALTAIH Bus (now known as the S-100 Bus) to generate the VKT functions internally to the microcomputer. One such company, Pro- cessor Technology, Inc., offered a Video Display Moault (VDM-1), which provided all the necessary functions to display alphanumerics directly on a TV monitor. The char- acter memory was a 1K RAM located on the VDM-1 board it- self. The software that was provided with the VDM-1 tooK care of all the housekeeping needed to organize the memory into lines of text; to provide scrolling; and to enable reverse video. As time passed, it became apparent that the power of this microcomputer, just as its bigger brother the mini- computer, was in its ability to manipulate and display data. The VDM-1 could be used to display only alphanumer- ic characters; tabular data; or, at best, a rather crude graph. Since the VDM-1 page format was 64 characters per row and 16 rows per page, only a 61 X 16 matrix could be utilized for graphics. This left a great deal of machine capability unutilized. A dot plotter could be used to generate the output needed to display data in a graphic format. Dot matrix -5- plotters and line (vector) plotters are common throughout industry to produce just the kind of graphic representa- tion of data that the microcomputer Is capable of generat- ing; however, afs with a commercial VKT, the cost is prohi- bitive. A study of the VDM-1 showed [6] that there was actually a very fine dot matrix being generated on the TV screen. The dot matrix that was required to display a single char- acter was 9 dots wide by 13 dots high, and even though there were only 16 lines of 64 characters, the VDM-1 was generating a 576 X 208 dot matrix to display the 102^ characters per frame. Although these dots are not indivi- dually addressable in the VDM-1, it seemed possible to construct circuitry to create a display in which each dot (or pixel) would be individually controllable and stored in a single bit in memory; they would then be displayed as a dot matrix on the TV screen.