1:4 demultiplexer routing one input to four — multiplexers and decoders
exam standardthe mux run backwards
Answer
Y0 = 0, Y1 = 0, Y2 = 1, Y3 = 0
Why this example is worth doing
A demultiplexer is a decoder whose outputs are gated by a data line, and it is the inverse of the multiplexer: one input, many outputs, select chooses which one gets the data. The page pairs it with the mux to make the symmetry explicit, and notes that mux-and-demux pairs are how a single wire is shared between many sources and destinations — the whole basis of time-division multiplexing.
Try your own input in the Multiplexers & decoders. Multiplexers from 2:1 to 16:1 and decoders from 2:4 to 4:16, with the selection logic derived.
How the answer is reached
The probed row
S1 = 1, S0 = 0, D = 1
Output table
| S1 | S0 | D | Y0 | Y1 | Y2 | Y3 |
|---|---|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 1 | 1 | 0 | 0 | 0 |
| 0 | 1 | 0 | 0 | 0 | 0 | 0 |
| 0 | 1 | 1 | 0 | 1 | 0 | 0 |
| 1 | 0 | 0 | 0 | 0 | 0 | 0 |
| 1 | 0 | 1 | 0 | 0 | 1 | 0 |
| 1 | 1 | 0 | 0 | 0 | 0 | 0 |
| 1 | 1 | 1 | 0 | 0 | 0 | 1 |