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
The truth table is shown below:
|s1||s2||Output 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.
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