The circuit of Figure 9-80 shows how an eight-input MUX can be used to generate a four-variable logic function, even though the MUX has only three SELECT inputs. Three of the logic variables A, B, and C are connected to the SELECT inputs. The fourth variable D and its inverse D are connected to selected data inputs of the MUX as required by the desired logic function. The other MUX data inputs are tied to a LOW or a HIGH as required by the function.

(a) Set up a truth table showing the output Z for the 16 possible combinations of input variables.

(b) Write the sum-of-products expression for Z and simplify it to verify that

Figure 9-80

Transcribed Image Text:

Z = CBA + DCBA + DCBA