# ECE 301 – Digital Electronics Multiplexers and Demultiplexers (Lecture #12)

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ECE 301 – Digital Electronics Multiplexers and Demultiplexers (Lecture #12)

ECE 301 - Digital Electronics2 Multiplexers

ECE 301 - Digital Electronics3 Multiplexer A multiplexer switches (or routes) data from 2 N inputs to one output, where N is the number of select (or control) inputs. A multiplexer (mux) is a digital switch.

ECE 301 - Digital Electronics4 Multiplexer: 2-to-1 2 inputs 1 output 1 select S = 0 selects I 0 S = 1 selects I 1 Y = (I 0.s') + (I 1.s)

ECE 301 - Digital Electronics5 Multiplexer: 2-to-1 with Enable

ECE 301 - Digital Electronics6 Multiplexer: 4-to-1 Y = (I 0.s 1 's 0 ') + (I 1.s 1 's 0 ) + (I 2.s 1 s 0 ') + (I 3.s 1 s 0 ) Two select signals

ECE 301 - Digital Electronics7 0 w 0 w 1 0 1 w 2 w 3 0 1 f 0 1 s 1 s Multiplexer: 4-to-1 Select signal for first level of decoders Select signal for second level of decoders 2-to-1 Muxes

ECE 301 - Digital Electronics8 Multiplexer: 16-to-1

ECE 301 - Digital Electronics9 Designing Logic Circuits using Multiplexers Multiplexers

ECE 301 - Digital Electronics10 Mux: Designing Logic Circuits Each row in a Truth Table corresponds to a minterm – N-input Truth Table Each minterm can be mapped to a multiplexer input – N-input Multiplexer For each row in the Truth Table, where the output of the function is one (F = 1), – Set the corresponding input of the multiplexer to 1

ECE 301 - Digital Electronics11 Given the following Truth Table: Design a logic circuit to implement this function, using a 4-to-1 Multiplexer. Mux: Designing a Logic Circuit 0 1 0 0 1 1 1 0 1 fs 1 0 s 0 1 0

ECE 301 - Digital Electronics12 Exercise: Design a circuit, using a 4-to-1 Mux to realize the Boolean expression given below. F X,Y =  m(0,2) Mux: Desiging a Logic Circuit

ECE 301 - Digital Electronics13 Designing Logic Circuits using Multiplexers more efficiently. Multiplexers

ECE 301 - Digital Electronics14 Mux: Designing Logic Circuits Efficiently Each row in a Truth Table corresponds to a minterm – N-input Truth Table A product term of N-1 variables can be mapped to each of the multiplexer inputs – (N-1)-input Multiplexer For the rows in the Truth Table, – Group N-1 highest order inputs into pairs – Define the output of each pair using the N th input

ECE 301 - Digital Electronics15 Mux: Designing a Logic Circuit

ECE 301 - Digital Electronics16 Mux: Designing a Logic Circuit

ECE 301 - Digital Electronics17 Exercise: Design a circuit, using a 4-to-1 Mux to realize the Boolean expression given below. F X,Y,Z =  m(1,2,3,6) Mux: Designing a Logic Circuit

ECE 301 - Digital Electronics18 Demultiplexers

ECE 301 - Digital Electronics19 Demultiplexer A demultiplexer switches (or routes) data from one input to 2 N outputs, where N is the number of select inputs. A demultiplexer (mux) is also a digital switch. A demultiplexer performs the opposite function of a multiplexer.

ECE 301 - Digital Electronics20 Demultiplexer: 1-to-4 I s1s1 s0s0 O0O0 O1O1 O2O2 O3O3 0 1 2 3 S1S1 S0S0 O0O0 O1O1 O2O2 O3O3 00I000 010I00 1000I0 11000I O 0 = S 1 '.S 0 '.I O 1 = S 1.S 0 '.I O 2 = S 1 '.S 0.I O 3 = S 1.S 0.I

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