Decoder

Decoder vs. DEMUX

3-8 decoder: 3 data inputs, 8 outputs

1-8 DEMUX: 1 data input, 3 control inputs, 8 outputs

Add enable control bit to decoder:

e = 0: all outputs are 0

e = 1: behaves like regular decoder

Data inputs of a decoder correspond to the control bits of a DEMUX

Enable input of a decoder corresponds to the data bit of a DEMUX

The two circuits are identical.