Page 83 - Handout Digital Electronics
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Figure 20: A 4-1 multiplexer logic circuit
The Boolean expression for F is found by tracing the inputs Do – D3 and the control setting A and B
from the inputs of the AND gates and OR gate for example:
F = ABDo + ABD1 + ABD2 + ABD3 . The operation of the multiplexer is also best described by the
truth table. (See multiplexer truth table below).
Truth Table
A B F
0 0 Do
0 1 D1
1 0 D2
1 1 D3
From the truth table it is also clear that if the control setting of A and B are set to AB = 00, the Do input
line will be selected and output at F, will appear a 0 or a 1.
For example, show that if the control settings A and B are set to AB =10, then the input line D2 will be
selected.
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