Multiplexers as general-purpose logic (cont'd)

• Implementing a function of n variables using a 2n-1 :1 mux

  • n-1 control variables S0 – Sn – 1
  • One data variable Sn
  • Four possible values for each data input: 0, 1, Sn, Sn'
  • Example: F(A,B,C,D) implemented using an 8:1 mux

Choose A,B,C as control variables

Choose D as a data

variable

01234567

1D01D'DD'D'

A

8:1 MUX

B

C

F

D

1 0 1 1

1 0 0 0

1 1 0 1

0 1 1 0

AB

CD

A

00

01

11

10

00

01

11

10

C

B

S2

S1

S0

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