Multiplexer

Multiplexer Also called as Data Selector. m control signals Also called as Data Selector. Multiplex means Many into one. n i/p signals 1 o/p signal Multiplexer It is a combinational logic circuit Multiplexer is a circuit with many inputs and only one output. i.e. it accepts several data inputs and allows only one of them AT A TIME to get through to the output The routing of desired data input to output is controlled by SELECT (CONTROL) LINES.

Above diagram is of n:1 multiplexer with n input lines, m control lines and 1 output line. Here 2m = n So we can have 2:1 MUX ;with 1 control line 4:1 MUX ;with 2 control line 8:1 MUX ;with 3 control line 16:1 MUX ;with 4 control line

2:1 Multiplexer Circuit Diag. Inputs Output S0 D0 1 D1 Here the 2: 1 MUX has two I/P lines D0 and D1 and one select (control) line S0 When S0 =0 then output= D0 When S0 =1 then output= D1

4:1 Multiplexer Circuit diagram and truth table of 4:1 MUX are shown below: Inputs Output S1 S0 D0 1 D1 D2 D3

Assignment: Draw circuit diagram and write the truth table of 8:1 Multiplexer and 16:1 multiplexer.

realizations of a 4-to-1 multiplexer from a decoder, AND gate and an OR gate:

Demultiplexer Also called as Data distributor. m control signals Also called as Data distributor. Demultiplex means one to Many. 1 i/p signals n o/p signal Demultiplexer Demultiplexer is a circuit with one input and many outputs. i.e. it accepts one data input and steer the input signal to one of the output line. The routing of data input to one of the output is controlled by CONTROL SIGNALS. The circuit has 1 i/p signal, m control signals & n o/p signals

Demultiplexer is exactly reverse of multiplexer. Above diagram is of 1:n demultiplexer. Relationship b/w m & n is given by 2m = n where m = no. of control lines, n = no. of output lines So we can have 1:2 DEMUX ;with 1 control line 1:4 DEMUX ;with 2 control line 1:8 DEMUX ;with 3 control line 1:16 DEMUX ;with 4 control line

1:2 Demultiplexer Circuit Diag. Here the 1:2 DEMUX has 2 O/P lines Y0 and Y1 and one select (control) line S0 When S0 =0 then output= Y0 When S0 =1 then output= Y1

1:4 Demultiplexer Circuit diagram and truth table of 1:4 DEMUX are shown below: Inputs Output S1 S0 Y0=D 1 Y1=D Y2=D Y3=D

Assignment: Draw circuit diagram and write the truth table of 1:8 Demultiplexer and 1:16 Demultiplexer.

Applications A very common application for this type of circuit is found in computers, where dynamic memory uses the same address lines for both row and column addressing. A set of multiplexers is used to first select the row address to the memory, then switch to the column address