Wednesday, 15 February 2012

Multiplexers


  • It is a combinatorial circuit, which select one out of many input lines
  • Multiplexer consists of data input lines, selection inputs and an output line.
  • Depending on selection input lines one of data inputs is sent to output line
  • If 2n input lines need to be multiplexed then ‘n’ selection lines are required
4x1 multiplexer:
It multiplexes 4 data lines into one output line. It consists of 2 selection lines.
Boolean equation describing multiplexer is Y=D0S1’S0’+D1S1’S0+D2S1S0’+D3S1S0
Implementing Boolean function with multiplexer:
Implement F(C, B, A) =∑ (1, 3, 4, 6, 7)
With 4x1 multiplexer
In truth table two inputs needs to be selected as selection lines. Remaining one variable is used in data lines. For each of four combinations of selection line inputs, represent output in terms of remaining variable or 0 or 1.  The process is illustrated in figure.
 
Implementing Logic Gates with 2x1 multiplexer:
AND gate:
OR gate:
NAND gate:
NOR gate:
XOR gate:
XNOR gate:

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