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A 1 to 8 demultiplexer with data input Din, address inputs S0, S1, and S2, (with S0  as the LSB) and Y̅0 to Y̅ 7 as the eight de-multiplexed output, is to be designed using two 2 to 4 decoders (with enable input E and address input A0 and A1) as shown in the figure. Din, S0, S1, and S2 are to be connected to P, Q, R, and S but not necessarily in this order. The respective input connections to P, Q, R, and S terminals should be

A 1 to 8 demultiplexer with data input Din, address inputs S0, S1, and S2, (with S0  as the LSB) and Y̅0 to Y̅ 7 as the eight de-multiplexed output, is to be designed using two 2 to 4 decoders (with enable input E and address input A0 and A1) as shown in the figure. Din, S0, S1, and S2 are to be connected to P, Q, R, and S but not necessarily in this order. The respective input connections to P, Q, R, and S terminals should be Correct Answer D<span style="position: relative; line-height: 0; vertical-align: baseline; bottom: -0.25em;font-size:10.5px;">in</span>, S<span style="position: relative; line-height: 0; vertical-align: baseline; bottom: -0.25em;font-size:10.5px;">2</span>, S<span style="position: relative; line-height: 0; vertical-align: baseline; bottom: -0.25em;font-size:10.5px;">0</span>, and S<span style="position: relative; line-height: 0; vertical-align: baseline; bottom: -0.25em;font-size:10.5px;">1</span>

The given question is the expansion of

2 : 4 decoder to  1 : 8 decoder 

[ alt="GATE EC 2015 paper 2 Images-Q38.1" src="//storage.googleapis.com/tb-img/production/16/10/GATE%20EC_2015%20paper%202_Images-Q38.1.PNG" style="height:193px; width:212px">

We need to implement 1 : 8 DEMUX.

So, select lines of De-Mux should be mapped to address lines of the decoder.

The LSB of De-Mux should be connected to the LSB of address lines of the decoder

∴ R → S0 

and S→ S1

Input to both the decoder should be same so

∴ P → Din

∴ NOT gate along with OR gate in case to select one decoder at a time so Q → S2 

So,

P → Din

Q → S2

R → S0 

S→ S1

Hence option (4) is correct

Related Questions

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