A multiplexor is a combinational circuit having many inputs which allows for the outputting a single data input at a time by using selection input lines. A multiplexor has 2n data input lines , n select input lines and a single output.

Discussion by analogy : A Television remote control used to access 4 channels

Teacher describes a remote control with 2 buttons that can be toggled on and off to switch between 4 channels

A 4 to 1 multiplexor

4-to-1 multiplexer

The truth table is shown below:

s1s2Output at F

Note that the data from any input line can be either a 0 or 1 instantaneously depending what the input at a the time. For example, let us consider the situation where over the next 4 cycles of execution on a cpu that

  • dataline x­1 produces 0011 on each cycle respectively,
  • dataline x­2 produces 1100 on each cycle respectively; and
  • during cycles 1 and 2, s1 and s2 are 0 and 0 respectively
  • during cycles 3 and 4, s1 and s2 are 0 and 1 respectively

The resulting output at f over the four cycles are 0000.

That is, two bits of data from x­1, then two bits of data from x­2.

In sequence , we selected x1 for 2 consecutive cycles, then x2 for another 2 consecutive cycles.

Attribution to media used in this post

User:Mdd4696, Public domain, via Wikimedia Commons

© 2021  Vedesh Kungebeharry. All rights reserved. 

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