# gate design for four input and one output

Discussion in 'Homework Help' started by metanu, Apr 7, 2011.

1. ### metanu Thread Starter New Member

Apr 7, 2011
4
0
Hi all: I have a question on design a logic circuit that accepts a four digit binary input and creates a sign check bit. Here I am taking a,b,c and d as the value and getting only output as a. For four inputs and single output equivalent to one output of a. how do you design the gate?

2. ### debjit625 Well-Known Member

Apr 17, 2010
790
186
Create a truth table first post it here,design of the gate is not so hard after that.

Good luck

3. ### metanu Thread Starter New Member

Apr 7, 2011
4
0
the requirement is The sign bit is set to 1 if the left most bit of the data is 1.

the truth table is
A B C D s
0 0 0 0 0 0
1 0 0 0 1 0
2 0 0 1 0 0
3 0 0 1 1 0
4 0 1 0 0 0
5 0 1 0 1 0
6 0 1 1 0 0
7 0 1 1 1 0
8 1 0 0 0 1
9 1 0 0 1 1
10 1 0 1 0 1
11 1 0 1 1 1
12 1 1 0 0 1
13 1 1 0 1 1
14 1 1 1 0 1
15 1 1 1 1 1

here, s(a,b,c,d)=SUM (8,9.10,11,12,13,14,15)
which in k-map produces 'a'

4. ### Georacer Moderator

Nov 25, 2009
5,151
1,266
If your requirement is exactly what you stated at post #3, then all is good.
It looks too easy to be true though. Are you sure this is what you have to find?

5. ### metanu Thread Starter New Member

Apr 7, 2011
4
0
well, the problem is how to represent this
s(a,b,c,d)=SUM(a)
in a logic gate? Gates I can use are AND, OR and NOT.
Thanks

6. ### Georacer Moderator

Nov 25, 2009
5,151
1,266
You don't need a gate for that. You just drive "a" to the output. It's candy from a baby.

That's why I ask you if the question is different. It is just too easy.