# Digital Design Lab Help - Decoders

Discussion in 'Homework Help' started by meadowrag, Feb 24, 2014.

Feb 24, 2014
3
1
I realize that this must be a very basic question, but I'm new to all of this and thus far my instructors have actually been a bit standoffish when it comes to guidance, thus I turn to you.

This is what we have been given -

My partner and I are are number 1 under breadboard implementation.

I've read a few resources on decoders, and the main idea expressed was that you can use them in the form of n-to-2^n, or a BCD decoder, where only one of the outputs will be active.

I don't understand how that concept applies to our lab assignment. In what way do we need to use a decoder to build the given functions?

It looks as though we just have three outputs defined in terms of three variables.
Thus far the only thing my partner and I have built is a 3-way majority gate in a previous lab, and the above circuit looks more similar to that.

I just need some help understanding how a decoder fits in with all of this.

2. ### WBahn Moderator

Mar 31, 2012
18,093
4,918
Think of a 1 of 4 decoder.

You have two select inputs, A and B, and those put a HI on one of the four output lines as follows:

 A B Y0 Y1 Y3 Y3 0 0 HI LO LO LO 0 1 LO HI LO LO 1 0 LO LO HI LO 1 1 LO LO LO HI

What happens if you have your final output as F = Y1 OR Y2 ?

What logic function is implements by F(A,B)?

Feb 24, 2014
3
1
If F = Y1 or Y2 then F would be high when A=0B=1 or A=1B=0 I guess.

For some reason I can't even get the decoder to work.
I hooked it up to power and ground, hooked up my three inputs and 8 outputs, and hooked up an LED to test it.

Every output is high no matter what combination of inputs I use.
I have no idea what's wrong.