PPT Slide

3 – Combinational Logic Implementation

© 1996 Gaetano Borriello

Demultiplexers/decoders

• Decoders/demultiplexers: general concept

  • single data input, n control inputs, 2 outputs
  • control inputs (called “selects” (S)) represent binary index of output to which the input is connected
  • data input usually called “enable” (G)

37

n

1:2 Decoder:

O0 = G ? S’

O1 = G ? S

2:4 Decoder:

O0 = G ? S1’ ? S0’

O1 = G ? S1’ ? S0

O2 = G ? S1 ? S0’

O3 = G ? S1 ? S0

3:8 Decoder:

O0 = G ? S2’ ? S1’ ? S0’

O1 = G ? S2’ ? S1’ ? S0

O2 = G ? S2’ ? S1 ? S0’

O3 = G ? S2’ ? S1 ? S0

O4 = G ? S2 ? S1’ ? S0’

O5 = G ? S2 ? S1’ ? S0

O6 = G ? S2 ? S1 ? S0’

O7 = G ? S2 ? S1 ? S0

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