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page 238

20. SWITCHING LOGIC

• In logic based control, decisions are made based on available information.

20.1 BOOLEAN ALGEBRA

• Recall the basic rules of Boolean algebra,

page 239

Idempotent

A + A = A

Associative

( A + B ) + C = A + ( B + C )

Commutative

A + B = B + A

Distributive

A + ( B & C ) = ( A + B ) & ( A + C )

Identity

A + NULL = A

A & NULL = NULL

Complement

A + ~A = UNIVERSAL

A & ~A = NULL

DeMorgan’s

~( A + B ) = ~A & ~B

A & A = A

( A & B ) & C = A & ( B & C )

A & B = B & A

A & (B + C) = (A & B) + (A & C)

A + UNIVERSAL = UNIVERSAL

A & UNIVERSAL = A

~(~A) = A

~UNIVERSAL = NULL

~( A & B ) = ~A + ~B

Duality

interchange AND and OR operators, as well as all Universal, and Null sets. The resulting equation is equivalent to the original.

- Symbols for Boolean operations may look different AND, *, •, &

OR, + NOT, ~, A etc.

e.g.

A = B * ( C * ( D + E + C ) + F * C )

 

A = B * C ------------------------------------

Simplified Form

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