. Explain how the 3to8 decoder can be built using two 2to4 decoder which has active-high enable (E) input and?

Question

digital electronics

Answer 1

Tough to explain without a diagram but will try

3 to 8 means you have 3 inputs and 8 possible outputs
Bit2, Bit1, Bit0
000
001
010
011
100
101
110
111

So you use the MSB to enable one of the two 2-to-4 decoders.

Connect bits 1 and 0 to the inputs of BOTH 2-4 decoders
Connect the MSB (bit 2) to the enable input of decoder 1 via an inverter
Connect the MSB to the enable input of decoder 2 as is.

If the MSB =0 , decoder 1 will operate on the two inputs (the inverter will turn 0 to 1) and decoder 2 will be off
if the MSB=1 then decoder 2 will be on, and decoder 1 will be off