Programmable Logic Controllers. Su Chen Jonathon Lin
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Название: Programmable Logic Controllers
Автор: Su Chen Jonathon Lin
Издательство: Ingram
Жанр: Физика
isbn: 9780831193690
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If A is not 1, then A shall be 0; and if A is not 0, then A has the value of 1.
If A ≠ 1, then A = 0
If A ≠ 0, then A = 1
5.1.2Postulate 2
The result of the OR logic with a 0 or 1 follows the rules shown in Table 5.1.
5.1.3Postulate 3
The result of the AND logic with a 0 or a 1 follows the rules shown in Table 5.2.
Table 5.1: OR Logic with a 0 or a 1
Table 5.2: AND Logic with a 0 or a 1
5.2 Boolean Algebra Laws
There are a number of Boolean algebra laws that can be used to simplify the Boolean equations that represent logic circuits. Table 5.3 illustrates seven common Boolean algebra laws.
Table 5.3: Boolean algebra laws
5.2.1Commutative Laws
Commutative laws state that the order of two or more elements are commutative when they have either an AND or an OR relationship. This means that the order of two AND or OR elements does not change the output result. Figure 5.1 shows the commutative AND function of three elements A, B, and C. Figure 5.2 illustrates the commutative OR function of three elements A, B, and C.
Figure 5.1: Commutative AND function
Figure 5.2: Commutative OR function
5.2.2Associative Laws
Associative laws indicate that the grouping of elements can change without changing the result, provided that all of the operations between elements are the same relationship, either all ANDs or ORs. This means that the order of the AND or OR elements does not change the output result (Figure 5.3 and Figure 5.4).
Figure 5.3: Associative OR function
Figure 5.4: Associative AND function
5.2.3Distributive Laws
The distributive laws allow us to rearrange elements in combinations of AND and OR relationships. Often by rearranging elements, we can combine portions to simplify the circuits. It has two forms: AND-OR and OR-AND. Figure 5.5 shows an example of the distributive law of AND-OR combination, which has the form of:
A · (B + C) = A · B + A · C
Figure 5.6 shows an example of using the OR-AND combination of distributive law. The distributive OR-AND function has the following Boolean expression:
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