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Multiplexers (MUX)

For logic function realizations, instead of logic gates, Multiplexers can also be used

Consider a boolean function f={1,2,6,7}. Here input variables are A,B,C.

Multiplexer schematic for $ 8\times 1$ multiplexer is shown in figure 13.1

Figure 13.1: ($ 8\times 1$) multiplexer implementation of logic function $ f$
\includegraphics[width=2.5in]{lec16figs/1.eps}
Depending on the contorl input combination specfic input is connected to the single output of multiplexer.

$\displaystyle f=\overline{A} \overline{B}C+\overline{A}B\overline{C}+AB\overline{C}+ABC$ (13.1)

When $ 8\times 1$ multiplexer is used to implement the above function. We connect boolean logic '1' at the inputs corresponding to control inputs ABC= 1, 2, 4, and 6. For all other input boolean logic '0' is connected.

In case we take a $ 4\times 1$ multiplexer we can make $ BC$ as control input and then determine what should be connected at the inputs of multiplexer as shown below.

$\displaystyle BC=00$ $\displaystyle \Rightarrow f=0$ (13.2)
$\displaystyle BC=01$ $\displaystyle \Rightarrow f=\overline{A}$ (13.3)
$\displaystyle BC=10$ $\displaystyle \Rightarrow f=A+\overline{A}=1$ (13.4)
$\displaystyle BC=11$ $\displaystyle \Rightarrow f=A$ (13.5)

The realization is shown in figure 13.2 using a $ 4\times 1$ Mux.

Figure 13.2: Multiplexer ($ 4\times 1$) Implementation
\includegraphics[width=3.5in]{lec16figs/2.eps}

next up previous contents
Next: Flip-Flops and Latches Up: Other ways of realizing Previous: Other ways of realizing   Contents
ynsingh 2007-07-25