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Department of Communication Engineering, NCTU 1
Unit 8 Multiplexers, Decoders andProgrammable Logic Devices
Department of Communication Engineering, NCTU 2
8.1 Multiplexers
Department of Communication Engineering, NCTU 3
Logic Design Unit 8 MUXs, Decoders & PLDs Sau-Hsuan Wu
2-to-1 Multiplexer
0 1Z A I AI
Department of Communication Engineering, NCTU 4
Logic Design Unit 8 MUXs, Decoders & PLDs Sau-Hsuan Wu
4-to-1, 8-to-1 and 2n-to-1 multiplexers
0 1 2 3Z A B I A BI AB I ABI
0 1 2 7Z A B C I A B CI A BC I ABCI
2 1
0
n
k kk
Z m I
Department of Communication Engineering, NCTU 5
Logic Design Unit 8 MUXs, Decoders & PLDs Sau-Hsuan Wu
Logic diagram for 8-to-1
Department of Communication Engineering, NCTU 6
8.2 Three-State Buffers
Department of Communication Engineering, NCTU 7
Logic Design Unit 8 MUXs, Decoders & PLDs Sau-Hsuan Wu
Tri-state Buffers
Department of Communication Engineering, NCTU 8
Logic Design Unit 8 MUXs, Decoders & PLDs Sau-Hsuan Wu
Using tri-state buffer for data selection
Department of Communication Engineering, NCTU 9
8.3 Decoders and Encoders
Department of Communication Engineering, NCTU 10
Logic Design Unit 8 MUXs, Decoders & PLDs Sau-Hsuan Wu
3-to-8 line decoder The i th output is 1 if the input binary value is equal to i
Department of Communication Engineering, NCTU 11
Logic Design Unit 8 MUXs, Decoders & PLDs Sau-Hsuan Wu
4-to-10 line decoder
Department of Communication Engineering, NCTU 12
Logic Design Unit 8 MUXs, Decoders & PLDs Sau-Hsuan Wu
In general a n-to-2n decoder can generate the all 2n
minterms Because an n-input decoder generates all of the minterms
of n variables, n-variable functions can be realized byORing together selected minterm outputs from a decoder
Department of Communication Engineering, NCTU 13
Logic Design Unit 8 MUXs, Decoders & PLDs Sau-Hsuan Wu
An encoder performs the inverse function of a decoder E.g. 8-to-3 priority encoder If more that one input is 1, the highest number determines
the output D is 1 if any input is 1, otherwise d is 0
Department of Communication Engineering, NCTU 14
8.4 Read Only Memories
Department of Communication Engineering, NCTU 15
Logic Design Unit 8 MUXs, Decoders & PLDs Sau-Hsuan Wu
A read-only-memory (ROM) is a semiconductor devicethat stores an array of data
Once binary data is stored in the ROM, it can be read out,but cannot be changed
Department of Communication Engineering, NCTU 16
Logic Design Unit 8 MUXs, Decoders & PLDs Sau-Hsuan Wu
A ROM with n input lines and m output lines
Department of Communication Engineering, NCTU 17
Logic Design Unit 8 MUXs, Decoders & PLDs Sau-Hsuan Wu
A ROM basically consists of a decoder and a memoryarray
Department of Communication Engineering, NCTU 18
Logic Design Unit 8 MUXs, Decoders & PLDs Sau-Hsuan Wu
The decoder output select one of the words
Department of Communication Engineering, NCTU 19
Logic Design Unit 8 MUXs, Decoders & PLDs Sau-Hsuan Wu
Multiple output functions can be realized with ROM