Boolean algebra, logic diagrams and truth tables
Kjartan Halvorsen
April 15, 2020
AND and OR
a, b ∈ {0, 1}
AND OR
a b a AND b, ab a b a OR b, a + b
0 0 0 0 0 0
0 1 0 0 1 1
1 0 0 1 0 1
1 1 1 1 1 1
a b a
Closed circuit ⇔ 1
Open circuit ⇔ 0
b
a
ab a
a+b
b b
NAND and NOR
a, b ∈ {0, 1}
NAND NOR
a b a NAND b, a · b a b a NOR b, a + b
0 0 1 0 0
0 1 1 0 1
1 0 1 1 0
1 1 0 1 1
a a
a·b a+b
b b
Boolean algebra, contd
x, y , z ∈ {0, 1}
Property Dual
Properties of 0 and 1 x +0=x x ·0 = 0
x +1=1 x ·1 = x
Idempotency x +x =x x ·x = x
Complementarity x +x =1 x ·x = 0
Involution x =x
Commutative x +y =y +x x ·y = y ·x
Associative (x + y ) + z = x + (y + z) (xy )z = z(yz)
Distributive x · (y + z) = xy + xz x + yz = (x + y )(x + z)
Boolean algebra, contd
x, y ∈ {0, 1}
Theorem Dual
Absorption x + xy = x(1 + y ) = x x(x + y ) = x
Logic adjacency xy + xy = x(y + y ) = x (x + y )(x + y ) = x
De Morgan’s x + y = x ·y xy = x + y
DeMorgan’s theorem
From wikipedia
Simplify functions
1. f = (a + b)(a + c)
2. f = a + ab
Logic diagram → function
Determine the function represented by the logic diagrams
a a
b b
f f
c
a
c
a a
b b
f f
b̄
d
c
Function → logic diagram
Draw the diagram corresponding to the boolean function
1. f = (a + b)(a + c)
2. f = a + ab
Group exercise
1. Enter breakout room
2. One of you downloads and shares this presentation
3. Work together on the problems in the previous three slides
3.1 Simplify functions
3.2 Determine function from logic diagram
3.3 Draw logic diagram from function