Expert: Zlatko - 7/21/2011

Question
1.Draw the circuit for 3-to-8 line decoder.

Answer
What is the truth table for a three to 8 decoder? You have 3 inputs, A, B, C, and 8 outputs Q1 through Q8.
Under what states of A,B,C is Q1 on?
Under what states of A,B,C is Q2 on?

Here is a hint
Q1 = !A * !B * !C
Q2 = !A * !B * C
Come up with equations for Q1, Q2, Q3, ... Q8
Then implement those equations in logic gates.

If you see common logic, try to reuse gates. For example, notice that Q1 and Q2 both use !A*!B so you should use the same set of gates for both equations.

See also
http://www.lmgtfy.com/?q=three+to+eight+decoder

Remember, I am a software guy. Anything I say about hardware design could be wrong. Anything I say about software could be wrong too.

Good luck.