How are select lines connected to the DEMUXes in one level?

All DEMUXes at one level share the same select line

Each has a different select line

Only the first DEMUX in the level gets a select line

2076 Chaitra · 4 marks

1:16 DEMUX using 1:2 DEMUXes

Short answer

A 1:16 demux is built as a tree of 15 1:2 demuxes in four levels. The first level uses S3 to split the data into two groups of 8 outputs; subsequent levels use S2, S1, S0 to further divide until 16 outputs are obtained.

Implement 1:16 demultiplexer using 1:2 demultiplexer.

A 1:16 demultiplexer sends one data input $D$ to one of 16 outputs chosen by 4 select lines $S_3S_2S_1S_0$ . With 1:2 demultiplexers (one select line each) we build a tree of four levels.

Number of 1:2 DEMUXes: $1 + 2 + 4 + 8 = 15$ .

Level	DEMUXes	Select line	Outputs
1	1	$S_3$ (MSB)	2
2	2	$S_2$	4
3	4	$S_1$	8
4	8	$S_0$ (LSB)	16 ( $Y_0$ – $Y_{15}$ )

                         +-[1:2]-Y0,Y1
                +-[1:2]--+
                |        +-[1:2]-Y2,Y3
       +-[1:2]--+
       |        |        +-[1:2]-Y4,Y5
       |        +-[1:2]--+
       |                 +-[1:2]-Y6,Y7
D-[1:2]+
       |                 +-[1:2]-Y8,Y9
       |        +-[1:2]--+
       |        |        +-[1:2]-Y10,Y11
       +-[1:2]--+
                |        +-[1:2]-Y12,Y13
                +-[1:2]--+
                         +-[1:2]-Y14,Y15
   S3      S2       S1       S0

Working:

The first DEMUX sends $D$ to its upper output if $S_3 = 0$ (towards $Y_0$ – $Y_7$ ) or lower output if $S_3 = 1$ (towards $Y_8$ – $Y_{15}$ ).
Each level halves the group again using $S_2$ , then $S_1$ , then $S_0$ .
All DEMUXes at one level share the same select line.

Example: $S_3S_2S_1S_0 = 1011$ : level 1 goes to the lower half (8–15), level 2 ( $S_2=0$ ) to 8–11, level 3 ( $S_1=1$ ) to 10–11, level 4 ( $S_0=1$ ) to $Y_{11}$ . So $Y_{11} = D$ and all other outputs are 0.

✓ Answer checked by Claude Opus 5.5 (high effort)

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