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Implementation of Manchester and differential Manchester Digital encoding BY Nabil Ali Sharaf Murshed B.ENG in Electronic engineering,(communication section), Sudan University of Science &Technology,2002 A Dissertation Submitted in Partial fulfilment of the Requirements for The Degree of Master of Engineering In Computer Engineering and Networks Department of computer engineering Faculty of engineering &technology University of Gezira Supervisor: DR.ABDELRASOOL JABAR ALZUBIDI Jun 2008
?????? ??? : ????? ??????????????? ??????? ???? ??????? ????? ??????? ????? ?????? - Manchester (MANCH) and Differential Manchester (DMANCH) ????? ??????? ?????? ???????????? ????????? ????? ?????? ??????????? ??????? ??????? ????? ????????? ???????? ????? D-25 ??????????? ????? ?????????? ??????? ????? ?????? ??? ( ???? ????? ?????? ????????? ??????? ??????? ????? ?????? ????????? ???????? (D-flip-flops ???????????? ???? ???????? Darlington amplifier ??????? ???? ????????? ????????? ??????? ????? ?????? ??? D-flip-flops ????????? ???????? Darlington amplifier ????????? ????? ????????? ????? ????? ?????? (Two relays) (?????????? ??????? ?????? relays ) ( ????????? ?????? ?????? ????? ????? ????? ????? (ooscilloscope ??????? ??????? ????? ???????? ???????? ????? ????????? ?????????? ??????? ?????? ?????? ?????? ) (Manchester ????? ( ??????? ??????? ????? ????????? ???????? (Differential Manchester ??????? ?????? ??????? ???????? ????????? ???????? ???? ??????? ????????? ???? ??????? ??????? ????
Abstract This research includes the digital encoding techniques by designed an electronic circuit by which two types of digital encoding are achieved: Manchester encoding (MANCH) and Differential Manchester encoding (DMANCH) . The circuit was designed so that it can be connected to the computer via the D-25 connector where the computer represents the means to input data. The other two chips are Darlington amplifier chips so that the signal received from the D-flip flop is amplified by the Darlington amplifier chip which is connected to two relays representing the above two digital encoding techniques. The two relays are separately connected to an oscilloscope device which represents the output display unit for the data input to the computer after implementing one of the digital encoding techniques described above. This research allows us to make use of digital encoding practically by inspecting two types of digital encoding techniques
TABLE OF CONTENTS Dedication............................................................................................................... iii Acknowledgment......................................................................................................iv Abstract ....................................................................................................................v Abstract (Arabic)...................................................................................................vii Table of contents....................................................................................................viii List of Figures................................ ...................................................... ...............xiii List of Tables......................................................................................................... xiv List of abbreviations............................................................ ...................................xv CHAPTER ONE INTRODUCTION 1-1 introduction.........................................................................................................1 1-2 Background.........................................................................................................1 1-3 Approach.............................................................................................................2 1-4 Problem definition...............................................................................................2 1-5 Objective of the research................................................ ....................................3 1-6 Research outline..................................................................................................3
CHAPTER TWO DIGITAL TO DIGITAL ENCODING 2-1Introduction..........................................................................................................5 2.2Digital to digital encoding................................................................................... 6 2.2.1Unipolar..........................................................................................................7 2.2.2Polar................................................................................................................9 2.2.2.1nonreturn to zero (NRZ) encoding...................................... ...................10 2.2.2.2 Return to zero (RZ)...................................................................................12 2.2.2.3Biphase......................................................................................................13 2.2. 3 Bipolar........................................................................................................16 CHAPTER THREE MANCHESTER and DIFFERENTIAL MANCHESTER 3. Biphase¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­17 3.1 Manchester encoding......................................................................................17 3.1.1features............................................................................... ..........................17 3.1.2description....................................................................................................18 3.1.3 Summary......................................................................................................18 3.1.4 Conventions for representations of data........................................... ..........19 3.1.5 Shortcomings..................................................................................... .........20 3.1.6 In summary..................................................................................................21 3.2. Differential Manchester encoding................................................................... 21 3.3 Bi phase pros and cons............................................................................ .........25
CHAPTER FOUR INTERFACING TO COMPUTER 4.1 Interfacing concepts...........................................................................................26 4.1.1 Sensors as Input ¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­.28 4.1.2Analog to Digital Converter (A/D) ¡­¡­¡­¡­..¡­¡­¡­.¡­¡­¡­¡­¡­¡­¡­..29 4.1.3 Digital to Analog Converter (D/A)¡­¡­¡­ ¡­¡­¡­.¡­¡­¡­ ..¡­ ¡­¡­¡­..29 4.1.4 Interfacing outputs¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..29 4.1.5 Interfacing Digital Inputs¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­.¡­¡­¡­...................30 4.2 Serial Interfacing...............................................................................................32 4.2.1 Types of serial interface ¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­. 32 4.2.2 Interface the serial/RS232 port¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­.¡­¡­¡­¡­¡­. ..33 4.3 parallel Interface................................................................................................38 4.3.1 Introduction to parallel ports¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­................................38 4.3.2 Parallel Ports Types¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­......................39 4.3.3 Other Parallel Ports¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­...................39 4.3.4 PC 1/0 Controller Card¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­........40 4.3.5Demultiplexer (demux)¡­¡­¡­¡­¡­¡­¡­ ¡­¡­¡­¡­¡­¡­¡­¡­........... .........40 4.3.6 Hardware Properties¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­... ¡­.41 4.3.7 port addresses¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­.¡­. ¡­..42 4.4 PC Buses¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­....43 4.4.1 ISA bus¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..44
4.4.2 ELSA bus¡­¡­.¡­¡­¡­¡­¡­.¡­¡­¡­¡­¡­..¡­¡­¡­.¡­¡­¡­¡­¡­¡­¡­¡­¡­..46 4.4.3 PCI bus¡­¡­¡­¡­¡­.¡­¡­¡­....¡­¡­¡­..¡­¡­..¡­¡­.¡­¡­¡­¡­¡­¡­..........47 CHAPTER FIVE HARDWARE DESIGN 5.1 D-25 male connector.........................................................................................48 5.2 HD74LS373...................................................................................................... 49 5.2.1Features...................................................................................................... 50 5.2.2 Pin arrangement..................................................................................... 51 5.2.3function table............................................................................................51 5.2.4 Block Diagram.........................................................................................52 5.3ULN2003A............................................................................................. .......... 52 5.3.1Description.................................................................... ........................... 52 5.3.2 Pin connection........................................................... ..............................53 5.4 Relay..................................................................................................................54 5 .4.1Choosing a Relay................................................. .................................... 55 5.4.2Protection diodes for relays¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­.¡­¡­¡­¡­¡­¡­. 56 5.4.3Reed Relays¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­ ¡­¡­.¡­.. ¡­¡­.¡­¡­¡­¡­¡­¡­.57 5.4.4Relays and transistors compared¡­¡­¡­ ¡­¡­¡­¡­.. ¡­¡­¡­¡­¡­¡­¡­..58 5.4.5Advantages of relay¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­ ¡­.¡­¡­¡­¡­¡­¡­¡­¡­.58 5.4.6 Disadvantages of relays¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..¡­¡­¡­¡­.58 5.5 Design steps¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­ ¡­¡­¡­¡­¡­¡­¡­.¡­..¡­¡­ .....59 5.5.1step no 1¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..¡­..¡­¡­..59
5.5.2 step no 2¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­.¡­.....¡­60 5.5.3 step no 3¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..¡­60 5.5.4 step no 4 ¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..¡­...........61 5.5.5 step no 5¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..61 5.5.6 step no 6¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..¡­¡­¡­¡­¡­........62 CHAPTER SIX SOFTWARE 6.1. Definition¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..........................................64 6.2 Flowchart¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­.¡­¡­¡­... ..65 CHAPTER SEVEN RESULT AND DISCUSSION Result and Discussion..............................................................................................67 Practical circuit¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­.¡­¡­..68 CHAPTER EIGHT CONCLUSION AND RECOMMENDATION 8.1Conclusion ¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­.¡­¡­69 8-2 Recommendation ¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­... ..69 REFERENCES¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­71 APPENDIX A: CODE¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..¡­¡­¡­¡­.¡­¡­¡­¡­¡­¡­¡­¡­ .72 B: HD74LS373¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..¡­¡­¡­¡­¡­¡­¡­¡­..75 C:ULN2003A¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..83 .

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5270 (1) (1).docx

  • 1. Implementation of Manchester and differential Manchester Digital encoding BY Nabil Ali Sharaf Murshed B.ENG in Electronic engineering,(communication section), Sudan University of Science &Technology,2002 A Dissertation Submitted in Partial fulfilment of the Requirements for The Degree of Master of Engineering In Computer Engineering and Networks Department of computer engineering Faculty of engineering &technology University of Gezira Supervisor: DR.ABDELRASOOL JABAR ALZUBIDI Jun 2008
  • 2. ?????? ??? : ????? ??????????????? ??????? ???? ??????? ????? ??????? ????? ?????? - Manchester (MANCH) and Differential Manchester (DMANCH) ????? ??????? ?????? ???????????? ????????? ????? ?????? ??????????? ??????? ??????? ????? ????????? ???????? ????? D-25 ??????????? ????? ?????????? ??????? ????? ?????? ??? ( ???? ????? ?????? ????????? ??????? ??????? ????? ?????? ????????? ???????? (D-flip-flops ???????????? ???? ???????? Darlington amplifier ??????? ???? ????????? ????????? ??????? ????? ?????? ??? D-flip-flops ????????? ???????? Darlington amplifier ????????? ????? ????????? ????? ????? ?????? (Two relays) (?????????? ??????? ?????? relays ) ( ????????? ?????? ?????? ????? ????? ????? ????? (ooscilloscope ??????? ??????? ????? ???????? ???????? ????? ????????? ?????????? ??????? ?????? ?????? ?????? ) (Manchester ????? ( ??????? ??????? ????? ????????? ???????? (Differential Manchester ??????? ?????? ??????? ???????? ????????? ???????? ???? ??????? ????????? ???? ??????? ??????? ????
  • 3. Abstract This research includes the digital encoding techniques by designed an electronic circuit by which two types of digital encoding are achieved: Manchester encoding (MANCH) and Differential Manchester encoding (DMANCH) . The circuit was designed so that it can be connected to the computer via the D-25 connector where the computer represents the means to input data. The other two chips are Darlington amplifier chips so that the signal received from the D-flip flop is amplified by the Darlington amplifier chip which is connected to two relays representing the above two digital encoding techniques. The two relays are separately connected to an oscilloscope device which represents the output display unit for the data input to the computer after implementing one of the digital encoding techniques described above. This research allows us to make use of digital encoding practically by inspecting two types of digital encoding techniques
  • 4. TABLE OF CONTENTS Dedication............................................................................................................... iii Acknowledgment......................................................................................................iv Abstract ....................................................................................................................v Abstract (Arabic)...................................................................................................vii Table of contents....................................................................................................viii List of Figures................................ ...................................................... ...............xiii List of Tables......................................................................................................... xiv List of abbreviations............................................................ ...................................xv CHAPTER ONE INTRODUCTION 1-1 introduction.........................................................................................................1 1-2 Background.........................................................................................................1 1-3 Approach.............................................................................................................2 1-4 Problem definition...............................................................................................2 1-5 Objective of the research................................................ ....................................3 1-6 Research outline..................................................................................................3
  • 5. CHAPTER TWO DIGITAL TO DIGITAL ENCODING 2-1Introduction..........................................................................................................5 2.2Digital to digital encoding................................................................................... 6 2.2.1Unipolar..........................................................................................................7 2.2.2Polar................................................................................................................9 2.2.2.1nonreturn to zero (NRZ) encoding...................................... ...................10 2.2.2.2 Return to zero (RZ)...................................................................................12 2.2.2.3Biphase......................................................................................................13 2.2. 3 Bipolar........................................................................................................16 CHAPTER THREE MANCHESTER and DIFFERENTIAL MANCHESTER 3. Biphase¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­17 3.1 Manchester encoding......................................................................................17 3.1.1features............................................................................... ..........................17 3.1.2description....................................................................................................18 3.1.3 Summary......................................................................................................18 3.1.4 Conventions for representations of data........................................... ..........19 3.1.5 Shortcomings..................................................................................... .........20 3.1.6 In summary..................................................................................................21 3.2. Differential Manchester encoding................................................................... 21 3.3 Bi phase pros and cons............................................................................ .........25
  • 6. CHAPTER FOUR INTERFACING TO COMPUTER 4.1 Interfacing concepts...........................................................................................26 4.1.1 Sensors as Input ¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­.28 4.1.2Analog to Digital Converter (A/D) ¡­¡­¡­¡­..¡­¡­¡­.¡­¡­¡­¡­¡­¡­¡­..29 4.1.3 Digital to Analog Converter (D/A)¡­¡­¡­ ¡­¡­¡­.¡­¡­¡­ ..¡­ ¡­¡­¡­..29 4.1.4 Interfacing outputs¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..29 4.1.5 Interfacing Digital Inputs¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­.¡­¡­¡­...................30 4.2 Serial Interfacing...............................................................................................32 4.2.1 Types of serial interface ¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­. 32 4.2.2 Interface the serial/RS232 port¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­.¡­¡­¡­¡­¡­. ..33 4.3 parallel Interface................................................................................................38 4.3.1 Introduction to parallel ports¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­................................38 4.3.2 Parallel Ports Types¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­......................39 4.3.3 Other Parallel Ports¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­...................39 4.3.4 PC 1/0 Controller Card¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­........40 4.3.5Demultiplexer (demux)¡­¡­¡­¡­¡­¡­¡­ ¡­¡­¡­¡­¡­¡­¡­¡­........... .........40 4.3.6 Hardware Properties¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­... ¡­.41 4.3.7 port addresses¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­.¡­. ¡­..42 4.4 PC Buses¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­....43 4.4.1 ISA bus¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..44
  • 7. 4.4.2 ELSA bus¡­¡­.¡­¡­¡­¡­¡­.¡­¡­¡­¡­¡­..¡­¡­¡­.¡­¡­¡­¡­¡­¡­¡­¡­¡­..46 4.4.3 PCI bus¡­¡­¡­¡­¡­.¡­¡­¡­....¡­¡­¡­..¡­¡­..¡­¡­.¡­¡­¡­¡­¡­¡­..........47 CHAPTER FIVE HARDWARE DESIGN 5.1 D-25 male connector.........................................................................................48 5.2 HD74LS373...................................................................................................... 49 5.2.1Features...................................................................................................... 50 5.2.2 Pin arrangement..................................................................................... 51 5.2.3function table............................................................................................51 5.2.4 Block Diagram.........................................................................................52 5.3ULN2003A............................................................................................. .......... 52 5.3.1Description.................................................................... ........................... 52 5.3.2 Pin connection........................................................... ..............................53 5.4 Relay..................................................................................................................54 5 .4.1Choosing a Relay................................................. .................................... 55 5.4.2Protection diodes for relays¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­.¡­¡­¡­¡­¡­¡­. 56 5.4.3Reed Relays¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­ ¡­¡­.¡­.. ¡­¡­.¡­¡­¡­¡­¡­¡­.57 5.4.4Relays and transistors compared¡­¡­¡­ ¡­¡­¡­¡­.. ¡­¡­¡­¡­¡­¡­¡­..58 5.4.5Advantages of relay¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­ ¡­.¡­¡­¡­¡­¡­¡­¡­¡­.58 5.4.6 Disadvantages of relays¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..¡­¡­¡­¡­.58 5.5 Design steps¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­ ¡­¡­¡­¡­¡­¡­¡­.¡­..¡­¡­ .....59 5.5.1step no 1¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..¡­..¡­¡­..59
  • 8. 5.5.2 step no 2¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­.¡­.....¡­60 5.5.3 step no 3¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..¡­60 5.5.4 step no 4 ¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..¡­...........61 5.5.5 step no 5¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..61 5.5.6 step no 6¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..¡­¡­¡­¡­¡­........62 CHAPTER SIX SOFTWARE 6.1. Definition¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..........................................64 6.2 Flowchart¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­.¡­¡­¡­... ..65 CHAPTER SEVEN RESULT AND DISCUSSION Result and Discussion..............................................................................................67 Practical circuit¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­.¡­¡­..68 CHAPTER EIGHT CONCLUSION AND RECOMMENDATION 8.1Conclusion ¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­.¡­¡­69 8-2 Recommendation ¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­... ..69 REFERENCES¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­71 APPENDIX A: CODE¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..¡­¡­¡­¡­.¡­¡­¡­¡­¡­¡­¡­¡­ .72 B: HD74LS373¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..¡­¡­¡­¡­¡­¡­¡­¡­..75 C:ULN2003A¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­..83 .