# 2-to-1 and 4-to-1 Multiplexer

Discussion in 'Homework Help' started by 123456, Aug 2, 2006.

1. ### 123456 Thread Starter New Member

Jul 24, 2006
8
0
i'm sorry to borrow yr thread.
but i seriously need the truth-table of a 2-to-1 multiplexer & a 4-to-1 multiplexer.

let's say for 2-to-1,
S1, I0, I1

4-to-1,
S1, S2, I0, I1, I2, I3

many thanks.

2. ### Dave Retired Moderator

Nov 17, 2003
6,960
145

Take the 2-to-1 multiplexer as an example: you require there to be a control signal, C0, in addition to the above signals you describe.

If C0 = 0 then the output S1 will follow input 1, I0 and input 2, I1 is a don't care, i.e. it has no influence on the output.

If C0 = 1 then the output S1 will follow input 2, I1 and input 1, I0 is a don't care.

Hence the truth-table goes:

CO I0 I1 S1
0--0--0--0
0--0--1--0
0--1--0--1
0--1--1--1
1--0--0--0
1--0--1--1
1--1--0--0
1--1--1--1

The same logical arguement applies to the 4-to1 multiplexer, however there are two control signals, C0 and C1.

Dave