GO Classes DPP | GATE CS | Digital Logic | DEMUX

Answer 1

In a $1:4$ DEMUX, only one output receives $\mathrm{D}$ depending on the select lines.

When $\mathrm{S}_1\mathrm{S}_0=00$, output goes to $\mathrm{Y}_0$.

So, $\mathrm{Y}_0=\mathrm{S}_1'\mathrm{S}_0'\mathrm{D}$.

When $\mathrm{S}_1\mathrm{S}_0=01$, output goes to $\mathrm{Y}_1$.

So, $\mathrm{Y}_1=\mathrm{S}_1'\mathrm{S}_0\mathrm{D}$.

When $\mathrm{S}_1\mathrm{S}_0=10$, output goes to $\mathrm{Y}_2$.

So, $\mathrm{Y}_2=\mathrm{S}_1\mathrm{S}_0'\mathrm{D}$.

When $\mathrm{S}_1\mathrm{S}_0=11$, output goes to $\mathrm{Y}_3$.

So, $\mathrm{Y}_3=\mathrm{S}_1\mathrm{S}_0\mathrm{D}$.

Answer: C

Comments

Why can't option B possible? @GO Classes

Can't we take S0 as MSB? 

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no we cannot take it, because it is written that S1S0 which means MSB is S1

Answer 2

In a 1:4 Demux

{ 00,01,10,11 } so 

When S1S0=00S1​S0​=00, output goes to Y0Y0​.

So, Y0=S1′S0′DY0​=S1′​S0′​D.

When S1S0=01S1​S0​=01, output goes to Y1Y1​.

So, Y1=S1′S0DY1​=S1′​S0​D.

When S1S0=10S1​S0​=10, output goes to Y2Y2​.

So, Y2=S1S0′DY2​=S1​S0′​D.

When S1S0=11S1​S0​=11, output goes to Y3Y3​.

So, Y3=S1S0DY3​=S1​S0​D.

Answer: C