Discrete Mathematics

74 DISCRETE

MATHEMATIC..._---------------------------

Line

p

q

(p

1\

q)

Line

p q

(pvq)

1 1 1 I

1 1

1

1

2 1 0 0

2 1 0 1

3

0

I 0

3

0 1

1

5 0 0 0

5 0 0

0

This is the truth table for an OR gate.

We refer to input-output tables when discussing the input-output behaviour

of

a logic gate. This is

really just the same as a truth table, with a minor difference

of

using

ls

and

Os,

instead

of

true's and false's.

While the AND gates and

OR gates are shown with only two inputs, either one can have more than two

inputs. For example,

if

an AND gate has three inputs,

p,

q and

r,

then the output can be expressed with the

Boolean expression ...