# Logic functions with DEC and MUX

Discussion in 'Homework Help' started by #4><><0.-, Nov 25, 2012.

1. ### #4><><0.- Thread Starter New Member

Nov 25, 2012
1
0
Hello!

I am supposed to realize a logic function using a decoder and then the same function using a multiplexer.

I know how decs and muxs work, however I don't know how to use them to realize functions like this:

F=P'Q+Q'R'
G=(P'+R)*(P+Q)

P,Q,R->MUX->F,G

I read many articles and tried hard, but only figured out, how to do it more easily using logic gates and invertors, but we are not allowed to do it this way. We have to use decs and muxs. If I ask why can't we do it by gates, they tell me "Just because this is harder and I like watching you being hopeless." They never bring a thing into light

Can you help me with this task and tell me, how to solve it, please?

Thank you!

I'm sorry for my bad English.

2. ### WBahn Moderator

Mar 31, 2012
17,446
4,699
The reasons to understand how to do it this way include:

1) A better understanding of logic in general.

2) How to implement functions via look-up tables, which is how functions are implemented in many programmable logic technologies, including most FPGAs.

Now, think of how a MUX works. You put in a set of control inputs that select a specific data input to pass to the output. What if the data input for that channe is hard tied to either HI or LO?