ISPSoft User Manual

ISPSoft User Manual
• D2 := D0 + D1; (Statement)
This is a statement rather than an expression. The value of the arithmetic expression D0+D1 is
calculated, and the result of the operation is stored in D2. This statement is composed of the
expression D2 and the expression D0+D1.
Please refer to the following example. The program is mainly composed of two IF statements. When
the first IF statement is executed, the system evaluates the expression M0. If M0 is ON, the value of
the arithmetic expression D21+D22 will be calculated, and the result of the operation will be stored
in D20. When the second IF statement is executed, the system judges whether the value of the
arithmetic expression D0* (D1+D2) is equal to the value stored in D20. If the value of the arithmetic
expression D0* (D1+D2) is equal to the value stored in D20, the Boolean value is TRUE, and the
value of M1 is TRUE. If the value of the arithmetic expression D0* (D1+D2) is not equal to the value
stored in D20, the value of M1 is FALSE.
11.1.4 Operand and Operator
Operands and operators are basic elements of an expression. An operand is the object of an
operation, and an operator is a symbol or function representing an operation. For example, in the
expression D0 + D1, D0 and D1 are operands, and + is an operator.
An expression can be composed of operands and operators. It can also be composed of a single
operand. The operands in an expression can be devices, symbols, or constants.
Rules of precedence affect which values form operands for which operators. If the operators in an
expression share the same precedence, the order of the operation is carried out from left to right.
The operands which can be used in a structured text in ISPSoft are listed below.
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