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Code Converters, Multiplexers and Demultiplexers
Chapter 8 Code Converters, Multiplexers and Demultiplexers 1
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Objectives You should be able to:
Describe the function of a decoder and an encoder. Design the internal circuitry for encoding and decoding. Use manufacturers’ data sheets to determine operation of IC decoder and encoder chips. 2
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Objectives (Continued)
Explain the procedure involved in binary, BCD, and Gray code conversion. Explain the operation of code converter circuits built with SSI and MSI ICs. Describe the function and uses of multiplexers and demultiplexers. Design circuits that employ multiplexer and demultiplexer ICs. 3
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Decoding Process of converting some code (binary, BCD, or hex) to a single output 4-bit BCD decoder Comprised of a combination of logic gates 8
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Decoding 3-Bit Binary-to-Octal Decoder Truth Tables 9
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Decoding Complete Octal Decoder (active LOW outputs) 10
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Decoding Octal Decoder Decoder ICs Also known as 1-of-8 decoder
Also known as 3-line-to-8-line decoder Decoder ICs 11
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Decoding Octal Decoder IC 74138 pin configuration and logic symbol. 12
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Octal Decoder IC Decoding 74138 logic diagram and function table 13
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Decoding 7442 BCD-to-DEC Decoder IC
1-of-10 decoder pin configuration and logic symbol 14
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Decoding 7442 BCD-to-DEC Decoder IC
1-of-10 decoder logic diagram and function table 15
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Decoding 74154 Hexadecimal Decoder IC
1-of-16 Decoder pin configuration and logic symbol 16
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Decoding 74154 Hexadecimal Decoder IC
1-of-16 Decoder logic diagram and function table 17
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Encoding Opposite process from decoding
Used to generate a coded output from a singular active numeric input line. 18
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Encoding Octal-to-binary and decimal-to-BCD encoders 19
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Encoding A truth table can be used to design encoders using combinational logic. 20
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Encoding A basic decimal-to-BCD encoder 21
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Encoding 74147 Decimal-to-BCD Encoder
Inputs and outputs are Active-LOW Note bubbles on logic symbols Priority encoder - highest input has priority 22
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Encoding 74147 Decimal-to-BCD Encoder logic symbol and function table
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Encoding 74148 Octal-to-Binary Encoder Eight active-low inputs
Three active-low outputs Priority encoder 24
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Encoding 74148 Octal-to-Binary Encoder logic symbol and function table
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Code Converters Convert a coded input into another form
BCD-to binary is a good example Computer program (software) MSI integrated circuits (hardware) 27
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Code Converters Software BCD-to-Binary conversion
Must develop an algorithm Weighting factor of 10 28
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Code Converters 74184 BCD-to-Binary Converter logic symbol
Hardware approach 29
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Code Converters Six-bit BCD-to-Binary Converter using 74184 30
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Code Converters BCD-to-binary for two BCD decades 31
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Code Converters BCD-to-binary for three BCD decades 32
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Code Converters 6 bit binary-to-BCD and 8 bit binary-to-BCD converters
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Code Converters BCD-to-Seven Segment Converters
4-bit BCD into a 7-bit code to drive display segments Useful in calculators and any application that requires a 7 segment display. The 7447 is a commonly used IC 34
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Code Converters Gray Code is used to indicate the angular position of a rotating machine. Varies by only 1 bit from one entry to the next 35
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Code Converters Gray Code 36
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Code Converters Conversion between binary and Gray code using exclusive-OR gates 37
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Multiplexers Funneling several data lines into a single one for transmission to another point Data select control determines which input is transmitted 38
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Multiplexers S0 and S1 determine which data is transmitted 39
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Multiplexers Logic diagram for a four-line multiplexer Figure 8-31 40
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Multiplexers Some popular TTL and CMOS multiplexers 40
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Multiplexers 74151 Eight-Line Multiplexer logic symbol
Note 3 data select inputs for 8 inputs (23 = 8) 41
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Multiplexers 74151 Eight-Line Multiplexer logic diagram 42
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Multiplexers Provide Combination Logic Functions
Multiplexers can be used to implement combinational logic circuits. A multiplexer can replace several SSI logic gates 43
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Demultiplexers Opposite procedure from multiplexing Data distributor
Single data input routed to one of several outputs 45
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Demultiplexers In this simulation file, the D waveform is routed to the Y outputs as determined by the data select inputs (S0 and S1). 45
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Demultiplexers 74139 Dual 4-line Demultiplexer logic symbol and logic diagram 46
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Demultiplexers 74139 connected to route an input signal to the 2a output 47
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Demultiplexers 74154 4-line-to16-line hexadecimal decoder
Used as a 16 line demultiplexer Connected to route a signal to the 5 output 48
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Demultiplexers Analog Multiplexer/Demultiplexer
4051, 4052, 4053 CMOS devices High-speed CMOS also available (74HCT4051) Function as either device since inputs and outputs are bidirectional Analog since outputs can be any value between positive and negative supplies (not just 0 and 1) 49
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Demultiplexers 4051 CMOS analog multiplexer /demultiplexer 50
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System Design Application
The as a memory address decoder 51
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System Design Application
The used to encode an active alarm 52
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74HCT4051 Staircase Generator
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74HCT4051 Staircase Generator
The voltage divider at the Y-inputs creates outputs at 8 different voltage levels.
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Multiplexed Display Application
Allows sharing of common ICs, components, and conductors Four-digit registered are multiplexed to a single-digit bus Display bus is multiplexed into the four-digit displays 56
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Multiplexed Display Application
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Summary Decoders can be used to convert a binary code into a singular active output representing its numeric value. Encoders can be used to generate a coded output from a singular active numeric input line. 59
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Summary ICs are available to convert BCD to binary and binary to BCD.
The Gray code is useful for indicating the angular position of a shaft on a rotating device, such as a motor. Multiplexers are capable of funneling several data lines into a single line for transmission to another point. 60
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Summary Demultiplexers are used to take a single data value or waveform and route it to one of several outputs. 61
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