B1-05a Digital Techniques / Electronic Instrument Systems PDF

MODULE 05 Category B1 Licence CASA B1-05a Digital Techniques / Electronic Instrument Systems I Copyright © 2024 Aviation Australia All rights reserved. No part of this document may be reproduced, transferred, sold or otherwise disposed of, without the written permission of Aviation Australia. CONTROLLED DOCUMENT 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 2 of 283 CASA Part 66 - Training Materials Only Knowledge Levels Category A, B1, B2 and C Aircraft Maintenance Licence Basic knowledge for categories A, B1 and B2 are indicated by the allocation of knowledge levels indicators (1, 2 or 3) against each applicable subject. Category C applicants must meet either the category B1 or the category B2 basic knowledge levels. The knowledge level indicators are defined as follows: LEVEL 1 Objectives: The applicant should be familiar with the basic elements of the subject. The applicant should be able to give a simple description of the whole subject, using common words and examples. The applicant should be able to use typical terms. LEVEL 2 A general knowledge of the theoretical and practical aspects of the subject. An ability to apply that knowledge. Objectives: The applicant should be able to understand the theoretical fundamentals of the subject. The applicant should be able to give a general description of the subject using, as appropriate, typical examples. The applicant should be able to use mathematical formulae in conjunction with physical laws describing the subject. The applicant should be able to read and understand sketches, drawings and schematics describing the subject. The applicant should be able to apply his knowledge in a practical manner using detailed procedures. LEVEL 3 A detailed knowledge of the theoretical and practical aspects of the subject. A capacity to combine and apply the separate elements of knowledge in a logical and comprehensive manner. Objectives: The applicant should know the theory of the subject and interrelationships with other subjects. The applicant should be able to give a detailed description of the subject using theoretical fundamentals and specific examples. The applicant should understand and be able to use mathematical formulae related to the subject. The applicant should be able to read, understand and prepare sketches, simple drawings and schematics describing the subject. The applicant should be able to apply his knowledge in a practical manner using manufacturer's instructions. The applicant should be able to interpret results from various sources and measurements and apply corrective action where appropriate. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 3 of 283 CASA Part 66 - Training Materials Only Table of Contents Numbering Systems (5.2) 11 Learning Objectives 11 Numbering Systems 12 Applications of Numbering Systems 12 Numbering Systems 12 Units and Numbers 13 Numbering Systems - Base 14 Positional Notation and Zero 16 Digital Numbering Systems 18 Binary Numbering System 19 Octal Numbering System 20 Hexadecimal Numbering System 21 Converting Between Numbering Systems 23 Binary to Decimal Conversion 23 Decimal to Binary Conversion 23 Octal to Decimal Conversions 26 Decimal to Octal Conversions 26 Hexadecimal to Decimal Conversions 28 Decimal to Hexadecimal Conversions 28 Numbering Systems Conversions Summary 30 Data Conversion (5.3) 32 Learning Objectives 32 Digital and Analogue Data 33 Definitions 33 Converting Between Analogue and Digital 33 Operational Amplifiers 35 The Op-Amp 35 Zero Level Detection 35 Non-Zero Level Detection 36 Non-Inverting Amplifier 37 Inverting Amplifier 38 Digital to Analogue Conversion 39 Digital-to-Analogue Converters 39 Binary Weighted Resistor DAC 39 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 4 of 283 CASA Part 66 - Training Materials Only R/2R Ladder DAC 41 R/2R Ladder DAC Operation 42 Analogue to Digital Conversion 44 Analogue to Digital Conversion Methods 44 Flash ADC 44 Flash ADC Encoder 47 Digital-Ramp ADC 50 Data Buses (5.4) 52 Learning Objectives 52 Data Transmission 53 Electric Power 53 Electrical Data Transmission 54 Digital Data Transfer 55 Serial Data Transfer 57 Parallel Data Transfer 58 Multiplexing 59 Aircraft Multiplex System 61 Data Bus Systems 64 Data Bus Connectors 65 Bus Controller 66 MIL–STD–1553 Data Bus 67 MIL-STD-1553 Data Words 68 MIL–STD–1553 Data Transfer 71 MIL–STD–1553 Specifications 74 MIL-STD-1773 74 Aeronautical Radio Incorporated 76 History of ARINC 76 ARINC 429 76 ARINC 429 Characteristics 77 ARINC 429 Schematic Diagram 78 ARINC 429 Specifications 80 ARINC 429 Data Transfer 81 ARINC 429 Words 83 ARINC 429 Data Types 85 ARINC 429 Labels 85 ARINC 629 86 ARINC 629 Interconnection 87 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 5 of 283 CASA Part 66 - Training Materials Only ARINC 629 Interfaces 88 ARINC 629 Data Bus Cable 90 ARINC 629 Message Structure 90 ARINC 629 Timing 92 ARINC 629 Timing Mode 93 Logic Circuits (5.5) 98 Learning Objectives 98 Boolean Logic 99 Representing Binary Quantities 99 Digital Signals and Timing Diagrams 100 Boolean Constants and Variables 101 Truth Tables 103 Simple Logic Gates 106 Logic Gates 106 OR Gates 106 AND Gates 108 NOT Gate (Inverter) 110 Combining Gates 112 Logic Circuits 113 Simple AND and OR Circuits 113 Inverters in Circuits 114 Logic Circuit Worked Examples 115 Compound Logic Gates 117 NOR Gate 117 NAND Gate 118 Exclusive-OR (XOR) 120 Exclusive-NOR (XNOR) 122 The Universal Gates 123 Buffers 124 Inverting Buffers (Inverter) 125 Alternate Inverter Symbol 126 IEEE Gate Symbols 126 Fabrication of Gates 127 Worked Logic Circuit Examples 128 Logic Circuit Example Problems 128 Logic Circuit Example Solutions 128 Logic Waveform Example Problems 129 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 6 of 283 CASA Part 66 - Training Materials Only Logic Waveform Example Solutions 129 Electrical Circuit Logic Examples 130 Flip-Flops and Latches 131 Flip-Flops 131 NAND Gate S-R Flip-Flops 132 NOR Gate S-R Flip-Flops 135 Flip-Flop Invalid and Initial States 137 S-R Flip-Flop Practical Usage 138 Application of Logic Circuits in Aircraft Systems 140 Emergency Electrical Power Logic (A-320; Example ONLY) 140 Overview (747 Scavenge Pump Control and Operation – Centre Wing) 141 Basic Computer Structure (5.6.1) 144 Learning Objectives 144 Computer Terminology 145 Basic Computer Operation 145 Binary Digits 145 Bits, Nibbles and Bytes 148 Integrated Circuits 150 Computer Hardware 154 Computer Software 155 Motherboard 156 Microcomputers 157 Computer Architecture 158 Computer Processors 160 Operating System 161 Memory Technologies 163 Memory Storage Technologies 163 Magnetic Core Storage 163 Dynamic Random-Access Memory 164 NAND Solid State Drive 165 Magnetic Tape Storage 165 Magnetic Disc Storage 166 Semiconductor Storage (Silicon Chip) 168 Memory Storage Devices 169 Computer Memory 169 Storage Device Classification 169 Primary Storage 170 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 7 of 283 CASA Part 66 - Training Materials Only Random-Access Memory 170 Read-Only Memory 171 Programmable Read-Only Memory 172 Erasable Programmable Read-Only Memory 173 Software Storage Mediums 174 Applications of Computer Based Technology in Aircraft Systems 176 Digital Aircraft Systems 176 Fibre Optics (5.10) 178 Learning Objectives 178 Fibre Optic Technology 179 Common Fibre Optic Technology Terms 179 Optical Fibre Cables 179 Optical Fibre Communications System 180 Basic Structure of an Optical Fibre 182 How Fibre Optic Cable Functions 183 Fibre Optic Operational Behaviour 185 Light Wave Propagation 185 Fibre Optic Cable Losses 186 Fibre Optic Cable Handling Precautions 189 Fibre Optic Terminations 191 Fibre Optic Splices 191 Fibre Optic Splices 191 Fibre Optic Couplers and Remote Terminals 196 Fibre Optic Couplers 196 Optical Fibre System Terminals 198 Optical Fibre Data Bus for Aircraft Systems 200 Advantages of Fibre Optic Data Communication 200 Disadvantages of Fibre Optic Data Communication 200 Aircraft Applications of Optical Fibre 202 Fibre Optic Data Bus 202 Flight Data Recording 203 Fibre Optics Gyroscopes 204 Electronic Displays (5.11) 206 Learning Objectives 206 Light Emitting Diodes in Aircraft 207 LED Fundamentals 207 Peak Wavelength Single-Coloured (Monochromatic) LEDs 207 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 8 of 283 CASA Part 66 - Training Materials Only Multi-Coloured and Bi-Coloured LEDs 208 Tri-Coloured LEDs 209 Seven-Segment LED Display 210 Alphanumeric LED Display 211 Dot Matrix LED Display 212 Organic LEDs 213 Liquid Crystal Displays 215 Polarisation 215 Liquid Crystal 215 Liquid Crystal Displays 216 Reflective LCD 220 Backlit LCD 222 Greyscale LCDs 223 Colour LCDs 224 Additive Colour Mixing 225 LCD Sub-Pixels 226 Colour LCDs 227 Cathode Ray Tube 228 Thermionic Emission – Edison Effect 228 Cathode Ray Tube 229 Electron Gun 230 The CRT Screen 231 CRT Operation Review 232 CRT Electron Beam Deflection 233 Electron Beam - Electrostatic Deflection 234 Summary of CRT Operation 239 CRT Handling and Disposal Safety 241 Coloured CRTs 243 CRT Screen Shadow Mask 243 Simultaneous Picture Formation 244 Sequential Scanning 246 Scanning Raster 247 Interlace Scanning 249 Aircraft CRTs 251 Care of Electronic Instrument Displays 251 Electrostatic Sensitive Devices (5.12) 253 Learning Objectives 253 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 9 of 283 CASA Part 66 - Training Materials Only Static Electricity 254 Generation of Static Charges 254 Induced Static Charges 254 Metal-Oxide-Semiconductor Devices 257 ESD Sensitivity 258 Device Sensitivity Classification 259 Identification of Equipment Susceptible to ESD 261 Classes of Devices 261 Circuit Cards 261 Types of ESD Damage 262 ESD Damage 264 ESD Handling Precautions 265 ESD Packaging 268 Approved ESD-Protective Packaging 268 Anti-Static Bags – Pink Poly 268 Anti-Static Bags – Metallic 269 Grid Tape 270 Conductive Transit Trays 271 Tote Boxes 272 Static Protection in DIP Tubes 273 Anti-Static Shipping Materials 275 Transportation of ESD Sensitive Devices 275 Shipping Boxes 275 Anti-Static Clamshells 275 Safe ESD Equipment and Work Practices 277 People are Prime Sources of ESD 277 ESD Grounding Strap 277 Anti-Static Gloves 278 Finger Cots 278 ESD-Safe Smocks and Lab Coats 279 Heel Strap Grounders 279 ESD-Safe Work Envelopes 280 Workshop Anti-Static Devices 280 ESD Protection Workplace Requirements 281 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 10 of 283 CASA Part 66 - Training Materials Only Numbering Systems (5.2) Learning Objectives 5.2.1 Identify the binary, octal and hexadecimal numbering systems (Level 1). 5.2.2.1 Recall how conversions from decimal to the binary, octal and hexadecimal numbering systems are performed (Level 1). 5.2.2.2 Recall how conversions from binary, octal and hexadecimal numbering systems to the decimal numbering system are performed (Level 1). 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 11 of 283 CASA Part 66 - Training Materials Only Numbering Systems Applications of Numbering Systems Computers are now employed wherever repeated calculations or the processing of huge amounts of data is needed. The greatest applications are found in aviation, military, scientific and commercial fields, ranging from mail sorting to engineering design and navigation around the globe. The advantages of digital computers include speed, accuracy and manpower savings. Often computers are able to take over routine jobs and release personnel for more important work, work that cannot be handled by a computer. People and computers do not normally speak the same language. Methods of translating information into forms that are understandable and usable to both are necessary. Humans generally speak in words and numbers expressed in the decimal number system, while computers understand only coded electronic pulses that represent digital information. © Lufthansa Aviation Training 2021 Numbering systems are used in all areas of aviation This topic will cover number systems in general, and binary, octal and hexadecimal (which we will refer to as hex) number systems specifically. Methods for converting numbers in the binary, octal and hex systems to equivalent numbers in the decimal system (and vice versa) will also be described. You will see that these number systems can be easily converted to the electronic signals necessary for digital equipment. Until now, you have likely only used one number system: the decimal system. You may also be familiar with the Roman numeral system even though you seldom use it. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 12 of 283 CASA Part 66 - Training Materials Only Numbering Systems Most numbering systems have certain things in common. These common terms will be defined using the decimal system as our base. Each term will be related to each number system as that number system is introduced. Each of the number systems covered is built around the following components: unit, number and base. © Aviation Australia Common numbering systems 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 13 of 283 CASA Part 66 - Training Materials Only Units and Numbers The terms unit and number, when used with the decimal system, are almost self-explanatory. By definition, the unit is a single object, that is, an apple, or a dollar, or a day. A number is a symbol representing a unit or a quantity. The figures 0, 1, 2 and 3 through 9 are the symbols used in the decimal system. These symbols are called Arabic numerals or figures. Other symbols may be used for different number systems. For example, the symbols used with the Roman numeral system are letters: V is the symbol for 5, X for 10, M for 1000 and so forth. We will use Arabic numerals and letters in the number system discussions. Creative Commons The Arabic numerals 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 14 of 283 CASA Part 66 - Training Materials Only Numbering Systems - Base The base of a number system tells you the number of symbols used in that system. The base of any system is always expressed in decimal numbers. The base of the decimal system is 10. This means there are 10 symbols – 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9 – used in the system. A number system using three symbols – 0, 1 and 2 – would be Base 3; four symbols would be Base 4; and so on. Remember to count the zero or the symbol used for zero when determining the number of symbols used in a number system. The base of a number system is indicated by a subscript (decimal number) following the value of the number. The following are examples of numerical values in different bases with the subscript to indicate the base. For example, 10102 is 1010 binary, 101010 is 1010 decimal and 101016 is hexadecimal, all of which represent totally different values. © Aviation Australia Base of binary, decimal and hexadecimal You should notice the highest value symbol used in a number system is always one less than the base of the system. In Base 10 the largest value symbol possible is 9; in Base 5 it is 4; in Base 3 it is 2. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 15 of 283 CASA Part 66 - Training Materials Only © Aviation Australia Numerals A unit is a single object or quantity, for example, a dollar, or a litre of fuel, or a day. A numeral is the symbol that represents a unit or quantity, for example, 5 = ♣ ♣ ♣ ♣ ♣. The base of a numbering system indicates how many symbols are used in the system. System Number of Symbols Symbols Base 10 10 0123456789 Base 8 8 01234567 Base 2 2 01 Base 16 16 0123456789ABCDEF © Aviation Australia The base of a number system is indicated by subscript 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 16 of 283 CASA Part 66 - Training Materials Only Positional Notation and Zero You must observe two principles when counting or writing quantities or numerical values: the positional notation and zero principles. Positional notation is a system in which the value of a number is defined not only by the symbol but by the symbol’s position. Let us examine the decimal (Base 10) value of 427. You know from experience that this value is four hundred twenty-seven. Now examine the position of each number: If 427 is the quantity you wish to express, then each number must be in the position shown. If you exchange the positions of the 2 and the 7, then you change the value. Each position in the positional notation system represents a power of the base, or radix. A power is the number of times a base is multiplied by itself. The power is written above and to the right of the base and is called an exponent. Aviation Australia Base 10 numbering system In the bottom example, the number 6348 is equal to 41210. Where the 2 in the upper number indicated 2 times 10, the 3 in the lower number equals 3 times 8, and so on, for the hundreds columns. Aviation Australia Base 8 numbering system 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 17 of 283 CASA Part 66 - Training Materials Only Just as important as positional notation is the use of the zero. The placement of the zero in a number can have quite an effect on the value being represented. Sometimes a position in a number does not have a value between 1 and 9. Consider how this would affect your next paycheque. If you were expecting a cheque for $605.47, you would not want it to be $65.47. Leaving out the zero in this case means a difference of $540.00. In the number 605.47, the zero indicates that there are no tens and is a very important numeral to include. Digital Numbering Systems The Base 10 system (Decimal) is the universal method of counting and recording values. The Base 2 system (Binary) is used by computers to perform all calculations and processes. It is the consequence of transistor state: either ON or OFF (1 or 0). The Base 8 system (Octal) is widely used in computer application sectors and digital numbering systems. Octal numerals can be easily converted from binary by grouping consecutive binary digits into groups of three (starting from the right). Thus an octal value represents 3 binary bits. For example, the binary representation for decimal 74 is 1001010. Two zeroes can be added at the left: (00)1 001 010, corresponding the octal digits 1 1 2, yielding the octal representation 112. The Base 16 system (Hexadecimal) is similar to octal with respect to ease of conversion from binary. A hexadecimal numeral represents four binary bits. The decimal numbering system is, of course, the system used universally. © Aviation Australia Binary converts more easily to octal and hexadecimal 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 18 of 283 CASA Part 66 - Training Materials Only Unlike analogue, which uses continuously changing values, digital uses discrete numerical values to represent waveforms. Those values are not represented by the familiar decimal numbering system that we use in our daily lives, but rather the binary number system. To represent 10 different values, a computer would need to incorporate 10 levels, for example, brightness of lights, voltages, clock- pulses and so on. A computer works only in digital, using zeros and ones. This is easily represented: something is either ‘on’ (1) or ‘off’ (0). So when you type a decimal number into your calculator, it converts it to digital, performs the calculation, and then converts the answer back into decimal for display. In order to comprehend how a computer functions, you must understand the different numbering systems. In addition to the decimal system, we will cover Base 2 (Binary), Base 8 (Octal) and Base 16 (Hexadecimal). As mentioned before, with one digit (a bit, short for binary digit), there are two possible values. With two bits, there are four possible values. With 3 bits, there are 8 possible values. With 4 bits (a nibble), there are 16 possible values, and so on. Terms Number of bits Representation Bit 1 1 Nibble 4 0101 Byte 8 0000 0101 Word 16 0000 0000 0000 0101 Long word 32 2 x word Very long word 64 4 x word © Aviation Australia Graphical representation of binary terms and representations 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 19 of 283 CASA Part 66 - Training Materials Only Binary Numbering System The binary numbering system is the base 2 numbering system. In the base 2 system only two symbols, 0 and 1, are used. Every numbering system can be defined through a table demonstrating the value of digits (increasing from right to left). For example, the decimal numbering system (base 10) looks as follows. The decimal system uses powers of 10 to determine the value of a position. The binary system uses powers of 2 to determine the value of a position. © Aviation Australia Decimal truth table Often the binary numbering system will need to be converted to decimal to be understood by humans. This is conversion is determined by the binary number truth table. Because each position is the base of the number lifted to a power, for example, 21, 22, 23, 24 and so on, we simply calculate the values and write them across a page. Below the values, record the number to be converted and then add each of the values which has a 1 in its column. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 20 of 283 CASA Part 66 - Training Materials Only Octal Numbering System Each octal numeral can be represented by three binary digits, and the two number systems are readily converted from one to the other by substitution. So 778 is followed by 1008, in a similar sequence as 9910 is followed by 10010. 1008 is quite a bit smaller than 10010. 1008 = 6410. The advantage is that a binary number sequence or readout can be displayed as an octal number, which can then be readily converted back to binary, for example, fault isolation. Instead of displaying 110 011 010 010 111 1102 on a readout, 6322768 can be displayed. This is far more easily written and remembered than the binary equivalent. Writing the binary number would increase the chances of transposing a digit while copying, plus it is simply a large unwieldy number, difficult to write and difficult to memorise. 6322768, by comparison, is more simply remembered. A common method of interpreting data in aircraft is to memory inspect a computer memory location and to interpret the data stored there. Of course, the data is stored digitally. Some aircraft may have computer systems which convert the data into useable information, but others will simply only provide the digital data as it is stored. It is then the engineer’s task to interpret the digital data. The octal numbering system has a base of 8. Numerals used are 0 1 2 3 4 5 6 7. 08 18 28 38 → 78 108 118 128 → 168 178 208 218 → 268 278 308 318 → 768 778 → 1008 Each octal digit represents three binary digits: Aviation Australia Octal numbering system 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 21 of 283 CASA Part 66 - Training Materials Only Hexadecimal Numbering System The hexadecimal number system is referred to as Base 16 and uses 16 unique symbols: 0–9 and A–F (the radix). This number system is useful because it can represent every byte (8-bits of binary) as two symbols. Hex uses the first 10 numbers of the decimal system: 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9. The number 10 has two digits, so in hexadecimal it is represented by the letter A, the number 11 by B, 12 by C, 13 by D, 14 by E and 15 by F. This gives 16 single-digit values: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F. To go higher, to the decimal number 16, we must use two digits, setting the first digit to 1 and increasing the second digit from 0 to F: 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 1A, 1B, 1C, 1D, 1E, 1F The decimal number 16 equals 10 in hexadecimal: (1 × 16) + 0. Continuing in the series, 17 (decimal) equals 11 (hexadecimal), 18 (decimal) equals 12 (hexadecimal), and so on until 31 (decimal), which equals 1F (hexadecimal). To increment to the number 32, we must change the first digit to 2 and increase the second digit from F to 0: 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 2A, and so on. So FF16 is followed by 10016 in a similar sequence as 9910 is followed by 10010, although 10016 is quite a bit larger than 10010. 10016 = 25610. Each hexadecimal digit represents four binary digits: Aviation Australia Hexadecimal numbering system 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 22 of 283 CASA Part 66 - Training Materials Only Converting Between Numbering Systems Binary to Decimal Conversion Converting from binary to decimal is relatively straightforward using the binary truth table. Example 1: 100012 (Binary Number) = 1710 (Decimal) Example 2: 110011012 (Binary Number) = 20510 (Decimal) © Aviation Australia Binary truth table and binary to decimal conversions When you are working with the decimal system, you normally do not use the subscript. Now that you will be working with number systems other than the decimal system, it is important that you use the subscript so that you are sure of the system being referred to. For example. you could say that 11001101 equals 205, and it would be assumed that the first value is binary and the latter is decimal. However, other numbering systems you cannot make this assumption, and therefore require the base annotation. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 23 of 283 CASA Part 66 - Training Materials Only Decimal to Binary Conversion There are two basic ways to do a decimal to binary conversion. You may decide which method you prefer to use. Decimal to Binary Conversion - Division (Method 1) This method repeatedly divides a decimal number by 2 and records the quotient and remainder. The remainder digits (a sequence of zeros and ones) form the binary equivalent. Example 1: Find the binary equivalent of the decimal number 19. Example 2: Find the binary equivalent of the decimal number 52. The digits in the remainder column form the binary equivalent of the decimal number. Once a decimal value is divided to it's maximum, write the binary value starting from the bottom value and from left to right. Aviation Australia Decimal to binary conversion For example, divide 19 by 2 (using whole number division) and you will find that 2 fits into 19, 9 times with 1 remainder. And then, 9 divided by two is 4 remainder 1, and so on until 1 is divided by 2, which cannot be done via whole number division and the value is zero. The final binary values for each decimal example (respectively) is 10011 and 110100. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 24 of 283 CASA Part 66 - Training Materials Only Decimal to Binary Conversion - Subtraction (Method 2) The subtraction method involves repeatedly subtracting powers of 2 from the decimal number. You need to have a list of powers of 2 up to the highest power of 2 that is less than or equal to the number you are converting. In our case, we are converting decimal 11, and the largest power of two less than or equal to 11 is 8 (23). Example: Convert 7510 to binary. Step 1: Start with the largest power of 2 which can be subtracted from the number to be converted. In this case the number is 75, so 64 is the largest truth table value that can be subtracted from 75. Annotate a 1 in the column under 64. Then subtract 64 from 75 to give 11. Step 2: What is the highest power of 2 that is subtractable from 11? The answer is 8. Annotate a 1 in the column under 8 and then calculate, 11 – 8 = 3. Step 3: What is the highest truth table value subtractable from 3? The answer is 2. Annotate a 1 in the column under 2 and then, finally, calculate 3 – 2 = 1. Step 4: Annotate a 1 in the column under 1, which leaves 1 – 1 = 0. Now fill in all the spaces between the 1s with 0s. © Aviation Australia Binary truth table for Seventy five base ten Therefore, 7510 = 1 001 0112. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 25 of 283 CASA Part 66 - Training Materials Only Binary/Decimal Exercises Complete the following exercises to practice converting from binary to decimal and from decimal back to binary. 1. Count from zero to 10 using binary numbers. 2. Convert 1112 to decimal. 3. Convert 510 to binary by the division method. 4. Convert 710 to binary by the division method. 5. Convert 1710 to binary by the subtraction method. 6. Convert 2410 to binary by the subtraction method. Octal to Decimal Conversions One method is to convert the octal number to binary, and then convert the binary number to decimal, as already explained by using the binary to decimal truth table. To convert straight across, use the octal truth table. octal 8 5 8 4 8 3 2 8 8 8 1 0 truth table 32 768 4 096 512 64 8 1 decimal value Example 1: 2 051 2 0 5 1 Example 2: 1024 + 0 + 40 + 1 = 1 065 362 415 3 6 2 4 1 5 98 304+24 576+1 024+256 + 8 + 5 = 124 173 Aviation Australia Octal to decimal conversion using the octal truth table 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 26 of 283 CASA Part 66 - Training Materials Only Decimal to Octal Conversions There are two basic ways to do decimal-octal conversion. You may find one or the other easier to understand and use. Decimal to Binary to Octal (Method 1) Convert the decimal number to binary as previously explained, and then substitute each set of three binary bits for an octal digit. The advantage of this method is that if you learn how to convert everything to and from digital, you can use digital as the base system and need only remember how to convert each system to and from digital. Of the three systems we describe for converting to and from binary, decimal is the only difficult method. Both octal and hexadecimal are easily converted to and from binary. Decimal to Octal Conversion – Division (Method 2) The division method works on the same basis as the decimal to binary conversions already covered, but in this case we divide by 8. All the remainders represent the octal number. Aviation Australia Decimal to octal conversion 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 27 of 283 CASA Part 66 - Training Materials Only Decimal/Octal Exercises Complete the following exercises to practice converting from binary to decimal and from decimal back to binary. 1. Count from zero to twelve using octal numbering 2. Convert 001 0102 to octal 3. Convert 101 1102 to octal 4. Convert 118 to decimal using the octal truth table 5. Convert 258 to decimal using the octal truth table 6. Convert 2710 to octal by the division method 7. Convert 38410 to octal by the division method Hexadecimal to Decimal Conversions One method of converting hexadecimal to decimal is to convert the hexadecimal number to binary and then convert the binary number to decimal, as already explained, by using the binary to decimal truth table. To convert straight across, use the hexadecimal truth table. The hexadecimal number 20, (2 × 16) + 0, equals 32 in decimal. The hexadecimal number 9C equals (9 × 16) + 12 = 156 in decimal. hexadecimal 16 4 16 3 2 16 16 16 1 0 truth table 65 536 4096 256 16 1 decimal value Example 1: B7F2 B 7 F 2 45 656+1792+240 +2 = 47 090 Example 2: 9B82A 9 B 8 2 A 589 824 +45 656+2 048 +32 +11 =636 970 Aviation Australia Hexadecimal to decimal conversion using a truth table 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 28 of 283 CASA Part 66 - Training Materials Only Decimal to Hexadecimal Conversions To convert a decimal number to hexadecimal, it is quite difficult to use the division method and divide by 16, but it will work. Remainders higher than 9 must be represented by the appropriate letter. Decimal to Hexadecimal Conversions - Division Method Aviation Australia Decimal to hexadecimal conversions An easier method is to first convert the decimal number to binary. Convert decimal to binary using either the division or subtraction method. Substitute each set of four binary bits with a hexadecimal numeral. Example conversion 18 36510 Decimal Number (18 365) 1 8 3 6 5 Base 10 Binary (grouped in 4 digits) 0100 0111 1011 1101 Base 2 Hexadecimal 4 7 B D Base 16 Decimal Number (7 985) 7 9 8 5 Base 10 Binary (grouped in 4 digits) 0001 1111 0011 0001 Base 2 Hexadecimal 1 F 3 1 Base 16 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 29 of 283 CASA Part 66 - Training Materials Only Decimal/Hexadecimal Exercises Complete the following exercises to practice converting from hexadecimal to decimal and from decimal back to hexadecimal. 1. Count from zero to twenty using hexadecimal numbering 2. Convert 0011 00102 to hexadecimal 3. Convert 1010 11112 to hexadecimal 4. Convert 516 to decimal using the hexadecimal truth table 5. Convert 5116 to decimal using the hexadecimal truth table 6. Convert 2710 to hexadecimal by the division method 7. Convert 38410 to binary, then hexadecimal Numbering Systems Conversions Summary The following text illustrates how to convert everything to binary and vice versa. Using this common language (binary), conversions may be simpler. Aviation Australia Summary of conversions 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 30 of 283 CASA Part 66 - Training Materials Only Numbering Systems Conversions Revision Exercises Complete the following exercises to practice converting between numbering systems. 1. Convert 87910 to hexadecimal 2. Convert DEAF16 to decimal 3. Convert 110 010 0112 to octal and hexadecimal 4. Convert 2516 to octal 5. Convert 43710 to octal 6. Convert 11 3248 to decimal 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 31 of 283 CASA Part 66 - Training Materials Only Data Conversion (5.3) Learning Objectives 5.3.1.1 Identify analogue data (Level 1). 5.3.1.2 Identify digital data (Level 1). 5.3.2 Recall the basic operation and function of operational amplifiers (S). 5.3.2.1 Recall the operation of analogue to digital converters (Level 1). 5.3.2.2 Recall the basic operation of digital to analogue converters (Level 1). 5.3.2.3 Recall the applications of analogue to digital converters (Level 1). 5.3.2.4 Recall applications of digital to analogue converters (Level 1). 5.3.2.5 Identify the analogue data inputs and digital data outputs of analogue to digital converters (Level 1). 5.3.2.6 Identify digital data inputs and analogue data outputs of digital to analogue converters (Level 1). 5.3.2.7 Recall the limitations of the various types of digital and analogue data (Level 1). 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 32 of 283 CASA Part 66 - Training Materials Only Digital and Analogue Data Definitions At a practical level, the difference between analogue data and digital data is in how the data is measured. Analogue data is continuous and aims to identify every nuance of what is being measured, while digital data uses sampling to encode what is being measured. Another way to consider it is that analogue is the unfiltered raw data and digital is filtered data for practical use. Converting Between Analogue and Digital Analogue-to-Digital Converters (ADC) and Digital-to-Analogue Converters (DAC) are used to interface computers to the analogue world so that a computer can monitor and control a physical variable. A typical system may include: Transducer ADC Computer DAC Actuator. An understanding of Op-amps used as comparators is required to understand the operation of ADCs and DACs and will be introduced in the following section. Aviation Australia Analogue-to-Digital Converter (ADC) and Digital-to-Analogue Converter (DAC) 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 33 of 283 CASA Part 66 - Training Materials Only Transducer The physical variable is normally a non-electric quantity. A transducer is a device that converts that physical variable into an electrical variable ADC The transducer’s electrical analogue output serves as the analogue input to the ADC. The ADC converts this analogue input into a digital output. The output consists of a number of bits that represent the analogue value. For example, the transducer may output an analogue voltage range of 800 to 1500 mV, which the ADC might convert to 01010000 (80) to 10010110 (150). Computer The digital representation from the ADC is processed by the computer. It may perform calculations or other operations and then give a digital output to manipulate the physical variable. DAC The digital output from the computer is converted to a proportional analogue voltage or current. For example, the computer may output a digital range between 00000000 and 11111111, which the DAC converts to a voltage ranging from 0 to 10 V. Actuator The analogue signal from the DAC is often connected to some device used to physically control or adjust the physical variable. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 34 of 283 CASA Part 66 - Training Materials Only Operational Amplifiers The Op-Amp Operational amplifiers are often used to compare the amplitude of one voltage with another. In this application, the op-amp is used in the open-loop configuration, with the input voltage on one input and a reference voltage on the other. © Aviation Australia Operational amplifier The term operational amplifier, or op-amp, refers to a class of high-gain DC-coupled amplifiers with two inputs and a single output. The modern Integrated Circuit (IC) version is typified by the famous 741 op-amp. Some of the general characteristics of the IC version are: High gain, on the order of a million High-input impedance, low-output impedance Used with split supply (usually +/- 15 V) Used with feedback, with gain determined by the feedback network. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 35 of 283 CASA Part 66 - Training Materials Only Zero Level Detection One application of an op-amp used as a comparator is to determine when an input voltage exceeds a certain level. Note in the illustration that the inverting input is grounded to produce a zero level and that the input signal is applied to the non-inverting input. Aviation Australia Zero level detection Because of the high open-loop voltage gain, a very small difference between the two inputs drives the op-amp into saturation, causing the output voltage to go to its limit. For example, consider an op-amp with a gain of 100 000. A voltage difference of only 0.25 mV between the inputs could produce an output voltage of 25 V if the op-amp were capable. However, since most op-amps have a maximum output voltage of +/- 15 V because of their DC supply voltages, the device would be driven into saturation. The wave shape illustration shows the result of a sine wave input voltage applied to the non-inverting input of the zero-level detector. When the sine wave is negative, the op-amp output is at its maximum negative level. When the sine wave input crosses zero (going positive), the amplifier is driven to its opposite state and the output goes to its maximum positive level. The zero-level detector can be used as a squaring circuit to produce a square wave from a sine wave. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 36 of 283 CASA Part 66 - Training Materials Only Non-Zero Level Detection The zero-level detector can be modified to detect voltages other than zero by connecting a fixed reference voltage to the inverting input as shown in diagram (a) using a battery. A more practical arrangement is shown in diagram (b) uses a voltage divider to set the reference voltage. A Zener diode can also be used to set the reference voltage. Aviation Australia (a) Battery reference, (b) Voltage divider reference, (c) Waveform As long as the input voltage (Vin) exceeds the reference voltage (VREF), the output goes to its maximum positive voltage. Non-Inverting Amplifier An op-amp is connected in a closed-loop configuration as a non-inverting amplifier with a controlled amount of voltage gain. Non-inverting amplifier 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 37 of 283 CASA Part 66 - Training Materials Only The input signal is applied to the non-inverting input (Vin +). The output is applied back to the inverting input (negative -) through the feedback circuit (closed loop) formed by Resistor input (R1) and Resistor feedback (R2). This creates negative feedback as follows. R1 and R2 form a voltage divider circuit which reduces Voltage out (Vout) and connects the reduced voltage to the inverting input. Inverting Amplifier The Inverting amplifier input signal is applied to the inverting input (2). The output is applied back to the inverting input (2) through the feedback circuit (closed loop) formed by Resistor input (R1) and Resistor feedback (Rf). This creates negative feedback using R1 and Rf as a voltage divider circuit. The voltage divider reduces Voltage out (Vout) and connects the reduced feedback voltage to the inverting input. Aviation Australia Inverting amplifier For equal resistors, the circuit has a gain of -1 and is used in digital circuits as an inverting buffer (also known an inverter). Therefore, an op-amp inverting amplifier with a gain of 1 serves as an inverting buffer. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 38 of 283 CASA Part 66 - Training Materials Only Digital to Analogue Conversion Digital-to-Analogue Converters One common requirement in electronics is to convert signals back and forth between analogue and digital forms. Most such conversions are ultimately based on a DAC or D/A converter circuit. Therefore, it is worth exploring just how we can convert a digital number that represents a voltage value into an actual analogue voltage. Digital input values on 1, 2, 4, and 8 are input to the op-amp via weighted resistors. The resultant voltage from the resistors is applied to the inverting input of the op-amp. Aviation Australia Binary weighted resistor DAC circuit 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 39 of 283 CASA Part 66 - Training Materials Only Binary Weighted Resistor DAC The illustrated circuit is the binary weighted resistor DAC shown in the previous section. It assumes a 4-bit binary number. The circuit uses +5 volts as a logic 1 and 0 volts as a logic 0. The circuit will convert the applied binary number to a matching (inverted) output voltage. In the following circuit, the digits 1, 2, 4 and 8 refer to the relative weights assigned to each input. Thus, 1 is the Least Significant Bit (LSB) of the input binary number, and 8 is the Most Significant Bit (MSB). Aviation Australia Binary Weighted Resistor DAC circuit If the input voltages are accurately 0 and +5 volts, then the 1 input will cause an output voltage of -5 × (4 k/20 k) = -5 × (1/5) = -1 V whenever it is a logic 1. Similarly, the 2, 4 and 8 inputs will control output voltages of -2, -4 and -8 V respectively. As a result, the output voltage will take on one of 10 specific voltages in accordance with the input BCD code. In the diagram below, the circuit is a binary weighted resistor DAC and truth table shows the conversion for a binary-weighted resistor DAC. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 40 of 283 CASA Part 66 - Training Materials Only Aviation Australia Binary weighted resistor DAC and truth table 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 41 of 283 CASA Part 66 - Training Materials Only R/2R Ladder DAC Binary weighted resistor DACs have some practical limitations. This is because there is a large difference in resistor values between the LSB and MSB. For example, in a 12-bit binary weighted resistor DAC – if the MSB resistor is 1 kΩ, then the LSB resistor will be over 2 MΩ. The problem is that when temperature varies, the resistance values over such a large range cannot maintain the correct ratios. The R/2R ladder overcomes this issue through its different circuit construction. The R/2R ladder uses only two resistance values and they are not greatly different. This means temperature variations have very little effect on the accuracy or the resistor ratios and therefore also have little effect on the voltage levels applied to the op-amp. © Aviation Australia R/2R ladder DAC (4-bit example) 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 42 of 283 CASA Part 66 - Training Materials Only R/2R Ladder DAC Operation The following diagram, is an example of a 4-bit R/2R Ladder DAC circuit with the inputs labelled. O/P is the output. Aviation Australia R/2R ladder DAC with binary input 1000 The fundamental operating principle of the R/2R ladder is that two parallel resistors of equal value have an overall circuit resistance of one half of the value of an individual resistor. So two 2xR resistors in parallel have an overall resistance of 1xR. Selecting inputs as either five volts or zero volts determines the configuration of the resistive circuit. In the R/2R ladder illustrated has a binary input of 0001 where the one equals five volts on S1. S1 is the most significant bit (MSB) and S4 is the least significant bit (LSB) so the input of 0001 illustrated represents a binary value of 10002. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 43 of 283 CASA Part 66 - Training Materials Only Analogue to Digital Conversion Analogue to Digital Conversion Methods Analogue to Digital Conversion (ADC) is a common interfacing process often used when a linear analogue system must provide inputs to a digital system. Many methods for ADC are available. We will cover the basic operation of two ADC types: Flash or simultaneous Digital-ramp or counter-type. The ADC process is generally more complex and time-consuming than the DAC process and many different methods have been developed. It may never be necessary to design or construct an ADC (they are available as complete packaged units). However, the techniques that are used provide insight into what factors determine an ADC’s performance. IN ADC OUT Creative Commons Analogue to digital converter 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 44 of 283 CASA Part 66 - Training Materials Only Flash ADC To convert a digital code to an analogue voltage, we only had to find a way to effectively assign an appropriate voltage to each bit, and then combine them. Is there an equally easy way of finding the digital code that corresponds to a given analogue voltage? © Aviation Australia Flash ADC Consider the very simple requirement to determine whether an analogue voltage was closest to 0, 1, 2 or 3 volts. The result is stored as a 2-bit binary number. The first step in making this determination might be a set of three comparators, connected as shown below. As the analogue voltage increases, the comparators will, one by one from the bottom up, change state from false to true. Of course, additional digital circuitry will be required to encode these signals into the corresponding digital number. But this circuit forms the sensing array that will determine directly which code will be closest to the actual analogue voltage. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 45 of 283 CASA Part 66 - Training Materials Only © Aviation Australia Flash ADC with encoder This approach will work and can be expanded to any number of steps for finer resolution of the analogue voltage. However, as you have probably already perceived, there is a problem with this approach in that the number of comparators required increases exponentially with the number of binary bits used to store the code. Using this approach to convert a 0 to 9-V range to a binary number will require nine comparators. A 4-bit binary number, counting from 0 to 15, requires 15 comparators. And a typical 8-bit circuit requires 255 comparators. This approach rapidly becomes too expensive for ordinary use, although it is practical if very high speed is required. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 46 of 283 CASA Part 66 - Training Materials Only Aviation Australia Flash ADC number of comparators grows exponentially with increasing binary bits 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 47 of 283 CASA Part 66 - Training Materials Only Flash ADC Encoder Due to the nature of the sequential comparator output states (each comparator saturating ‘high’ in sequence from lowest to highest), the same highest-order-input selection effect may be realised through a set of Exclusive-OR (XOR) gates. This allows the use of a simpler, non-priority encoder. The encoder circuit itself can be made from a matrix of diodes, demonstrating just how simply this converter design may be constructed. Not only is the flash converter the simplest in terms of operational theory, but it is the most efficient of the ADC technologies in terms of speed, being limited only in comparator and gate propagation delays. Unfortunately, it is the most component- intensive for any given number of output bits. Aviation Australia Flash ADC encoder An additional advantage of the flash converter, often overlooked, is the ability for it to produce a scaled output. For example, the diagram shows a float sensor in a fuel tank. Near the half-full point, the float moves almost vertically, giving a realistic readout of the contents. But at the extremities of close to full and empty, the float has more horizontal movement, giving a larger change in angle. This would result in a large change in the output voltage for little change in fuel level. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 48 of 283 CASA Part 66 - Training Materials Only Aviation Australia Analogue fuel sender By adjusting the value of the resistors, each change of Binary 1 at the output would represent the same change in fuel quantity, no matter the fuel level. With equal-value resistors in the reference voltage divider network, each successive binary count represents the same amount of analogue signal increase, providing a proportional response. For special applications, however, the resistor values in the divider network may be made unequal. This gives the ADC a custom, nonlinear response to the analogue input signal. No other ADC design is able to grant this signal-conditioning behaviour with just a few component value changes. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 49 of 283 CASA Part 66 - Training Materials Only 3-Bit Flash ADC Example Calculate the encoder inputs and digital outputs for the following analogue input voltage levels: Ex 1: VA = 2 volts Ex 2: VA = 4 volts Ex 3: VA = 5 volts Aviation Australia Flash ADC and truth table (3-bit digital output) 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 50 of 283 CASA Part 66 - Training Materials Only Digital-Ramp ADC A slower but much less expensive approach involves the use of a DAC and a single comparator. One of the simplest versions of the general ADC uses a binary counter as the register and allows the clock to increment the counter one step at a time until the comparator output (Vax ) ≥ the ADC input (Va). It is called a digital-ramp ADC because the waveform at Vax is a step-by-step ramp. It may also be referred to as a counter-type ADC. It contains a counter, a DAC, an analogue comparator and a control AND gate. The comparator output serves as the active-LO (low) End of Conversion (EOC) signal. The ADC circuit output is represented by the Counter IC outputs. The digital values produced by the Counter represent digital or binary numbers. The output illustrated is sent to the DAC and would also be sent to a display device. Aviation Australia Digital-ramp ADC 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 51 of 283 CASA Part 66 - Training Materials Only Data Buses (5.4) Learning Objectives 5.4.1 Describe the operation of data buses in aircraft systems (Level 2). 5.4.2 Describe the properties of data bus communication protocols including: MIL-STD 1553, ARINC 429, ARINC 629, Ethernet, AFDX (Level 2). 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 52 of 283 CASA Part 66 - Training Materials Only Data Transmission Electric Power In electricity delivery grids from power stations, power is transmitted over heavily constructed, thick power lines designed to carry very high voltages and a large electrical current. As the power is stepped down, so is the diameter of the wiring necessary to conduct it efficiently. Adapted from the National Energy Education Development Project (Public Domain) Electricity generation, transmission and distribution Different applications require differing amounts of power. For example, navigation light runs on 28-V DC, and so does an aircraft starter motor. The navigation light draws only a very small current, as is evident by the narrow-gauge wiring providing the power to it. The starter motor, on the other hand, draws a very high current, so a thick cable is necessary for the motor to operate efficiently and generate the torque required to turn over an aircraft engine. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 53 of 283 CASA Part 66 - Training Materials Only An example of a battery connected to an aircraft starter Both of these aircraft applications use electricity to perform work, hence there is significant current flow, necessitating appropriately sized wiring to carry the current required. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 54 of 283 CASA Part 66 - Training Materials Only Electrical Data Transmission An entirely different use for electricity is to transmit signals. Electricity is the ideal means to transmit information because it travels at the speed of light. Wiring utilised to transmit data carries only a negligible current, just sufficient to switch a transistor ON or OFF or to carry an audio signal, which is then amplified at its destination. This lesson deals entirely with transmission of data. Ideally no current flows on a digital data line, although in reality there is a small flow of current sufficient to at least forward and reverse bias semiconductor P and N junctions. But data bus lines are typically very small gauge, and the electrical signal transmitted over them is typically no higher than 5-V DC and looks similar to an AC sine wave, although without any uniformity or sequence. The information transmitted is actually all the 1s and 0s which represent data encoded as a digital signal. The data are sent in a regulated and uniform sequence between components, where computer processors at either end decode and utilise the data to produce the desired outputs, whether it be to display present latitude and longitude on a horizontal indicator or to drive a servo motor to regulate fuel flow to an engine. Aviation Australia Electrical signals through ICs and transmitted through data cables (or wireless) 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 55 of 283 CASA Part 66 - Training Materials Only Digital Data Transfer An ideal digital waveform is a square wave. The illustration below demonstrates an example of an ideal waveform (top) compared to how a waveform is likely to present in practice (bottom). Both waveforms represent 1010 0110. It is important to remember that the voltage produced is a result of the transistor switching ON and OFF, and transistors are not perfect in respect to instantaneously switching states from OFF to fully saturated. They are continually forward and reverse biased, so the wave shape is in reality more like a distorted AC sine wave as shown below. Although the wave shapes are not perfect, they do function as intended and any computer is a testament to how well the digital data transfer works. Aviation Australia Ideal vs practical digital signal In electronic digital systems, data in binary form is represented by the presence or lack of a voltage for each bit at the inputs and outputs of the various circuits. Typically binary 0 is represented by 0 V, and binary 1 is represented by 5 V. In practical systems, any voltage between 0 and 0.8 V (not sufficient to saturate a transistor) represents binary 0 and any voltage between 2 and 5 V represents a binary 1. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 56 of 283 CASA Part 66 - Training Materials Only Aviation Australia Practical data signal The clock pulse represented in the diagram is basically a representation of the operating speed of the data bus, and the transmitter and receiver are synchronised by the same clock pulse. When the transmitter is outputting a high, the receiver detects it and clocks it through as a 1 to processing circuitry. When data are next sampled by the receiver, the transmitter is outputting a low, and a 0 is clocked through to the processing circuitry. In digital, quantities are represented by voltages which have a wide tolerance (for example, 2–5 V for a 1) whereas in analogue, voltages must be exact – any deviation causes errors. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 57 of 283 CASA Part 66 - Training Materials Only Serial Data Transfer In digital computers, enormous amounts of data move between parts of the system. The two basic ways of doing this are by parallel data transfer and serial data transfer. In serial transfer, each bit of data is transferred from a store (or memory location; illustrated is 2 bytes of data, or 16 bits) in sequence over the same line. The data is triggered by clock pulses as explained in the previous slide, and the transmitter and receiver are synchronised with reference to the same clock pulse. When the data arrives at the receiver, it is sequentially stored in memory (2 bytes’ worth in this case) before being transferred to processing circuitry in the receiving component. The serial bus is one on which the data are transmitted sequentially, one word following another word. It is commonly used for long-distance transmissions. Advantages of serial data flow: less hardware, therefore less weight and space for an installation compared to parallel data transfer systems. Serial data transfer is typical of data-bus communications. Multiplexing is a typical method of speeding up the data transfer capacity of a serial data bus. Aviation Australia Serial data transfer 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 58 of 283 CASA Part 66 - Training Materials Only Parallel Data Transfer In parallel transfer, each bit is taken from a separate circuit (for example, a processing or calculating circuit) and is transmitted over a separate line. Advantage of parallel data transfer: much faster. In the example in the slide, it would be 16 times faster. When considering the time taken to download data from the internet over the serial connection, imagine how quickly everything would run if there was a parallel connection. The downside of parallel is, of course, you need much more hardware, which takes up space and increases weight, two things we do not want to do in an aircraft. Aviation Australia Parallel data transfer and associated hardware Serial data transfer is typical of data-bus communications, whereas once a signal is inside a computer, it is typically processed in parallel. A parallel bus typically interconnects the internal devices of a computer and has enough wires to transmit all bits of the word simultaneously. An 8-bit parallel bus is 8 times faster than the serial bus, and a 64-bit parallel bus is 64 times faster than its equivalent serial bus. 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 59 of 283 CASA Part 66 - Training Materials Only Multiplexing Multiplexing is combining two or more information channels onto a common transmission medium. On aircraft, multiplexing greatly decreases the number of wires carrying separate signals. Using a digital ‘time division’ technique, many different signals can be carried by one conductor. Benefits include a significant reduction in the weight of wire bundles and improved circuit reliability. Aviation Australia Multiplexing where two rotary switches are synchronised The basic principle of multiplexing is that two rotary switches are synchronised in their switching as they rotate around a series of contacts. The synchronised rotating contacts connect matching input and output lines in sequence, and data are transmitted over the common transmission line. © Aviation Australia Time domain multiplexing 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 60 of 283 CASA Part 66 - Training Materials Only In reality, multiplexing is usually done by logic gates responding in sequence to clock pulse signals. At the multiplexing end, the signal on each input line is sampled and passed to the common transmission line, when the inputs AND gate is clocked ON. The sequenced gate outputs are serially transmitted to the demultiplexer, where the inverse happens. As each AND gate is clocked on, it passes the signal that is on the transmission line at that time. This has the effect of transmitting eight separate inputs through to eight separate outputs over the same transmission line. In aircraft, analogue signals may be multiplexed, but they must first be converted to digital, transmitted over the multiplexer network and then converted back to analogue form once demultiplexed. In an aircraft, the sequencing controller is replaced by a Bus Controller (BC), which typically receives all the inputs and distributes outputs and processed data (after processing data from several inputs) to systems requiring the information. For example, it can distribute digitised data to be displayed on a multifunction display or calculated air density data for transmission to a thrust computer. Aviation Australia Logic gate multiplexing 2024-10-23 B1-05a Digital Techniques / Electronic Instrument Systems Page 61 of 283 CASA Part 66 - Training Materials Only Aircraft Multiplex System In the 1950s and 1960s, aviation electronics, referred to as avionics, were simple stand-alone systems. The navigation, communications, flight controls and displays consisted of analogue systems. Often these systems

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