# Boolean algebra > multiplexer in multisim

Discussion in 'Homework Help' started by eastmus, Dec 28, 2008.

1. ### eastmus Thread Starter New Member

Dec 28, 2008
9
0
Hello

I'm not so familiar with how mux works in multisim.
I need to draw the circuit of the following boolean algebra with an 8-to-1 Mux.

A(B+C)AB+BC(B+C)+AB

I drew this with logical ports to get the truthtable.
But I cant seem to get the same truthtable with a multiplexer >.<

Truthtable:
A B C X (where A,B,C are input and X is output)
0 0 0 0
0 0 1 0
0 1 0 0
0 1 1 1
1 0 0 0
1 0 1 0
1 1 0 1
1 1 1 1

Could someone help me out please?

2. ### silvrstring Active Member

Mar 27, 2008
159
0
Are you sure about the boolean expression you have to implement? If the truth table was given to you, then it simplifies to AB+BC.

3. ### eastmus Thread Starter New Member

Dec 28, 2008
9
0

Yes this is the expression given.

The truthtable however was not given.
And my simplified expression is AB+ACB+BC.
I compared both truthtables and they matched.

Now the only problem is to work with Mux in multisim and compare that truthtable

thanks

4. ### Ratch New Member

Mar 20, 2007
1,068
4
eastmus,

AB+ACB+BC = AB(C+C')+ACB+(A+A')BC=ABC+ABC'+ABC+ABC+A'BC
= ABC+ABC'+ABC+A'BC= AB(C+C')+(A'+A)BC=AB+BC

or even more simply, AB+ACB+BC=AB+ABC+ABC+BC+ AB(1+C)+(A+1)BC= AB+BC

Ratch

Last edited: Dec 29, 2008
5. ### eastmus Thread Starter New Member

Dec 28, 2008
9
0
wow thx ratch
i didnt even know.

that homework is like 2 months old and the teacher didnt tell me about making it more simple.

now how do i draw AB+BC with a mux in multisim ?

6. ### Ratch New Member

Mar 20, 2007
1,068
4
eastmus,

I don't know. I've never owned or used "multisim".

Ratch

7. ### DrNick Active Member

Dec 13, 2006
110
2
You can implement any boolean function with a MUX.

For instance you can implement a 2 input OR (A+B) using a 4-1 mux. What you do is put the OR truth table in to the 4 inputs of the MUX, and use A as the first select pin and B as the second select pin. When you select the individual bits of the truth table (that are the inputs to the MUX) you output the correct logic.

Now all you have to do is put your truth table in to an 8-1 MUX, and use A, B and C as the select pins. So take X and set D0 to 0 when ABC = 000. Then set D1 to 0 when ABC = 001, and continue with this until you have populated all of the D inputs with the values of X, and conntect A to A, B to B etc... that will implement your function with a MUX. You have to promise to figure out why this works since I told you how to do it .

8. ### eastmus Thread Starter New Member

Dec 28, 2008
9
0

mh thx for explaining
but im still not getting it >.< lol

i'll ask my teacher next week after the vacation