ISPSoft User Manual

Chapter 11 Structured Text
Data format
Example of an
expression
Result of an
Symbol Function
Precedence
operation
Operand
Expression Value
(Value of an
expression)
The
parenthetical
( )
part of an
expression is
Unspecified Unspecified (D0 + 6)* 3 33 Highest
calculated
first.
** Exponentiation Floating-point Floating-point
number number
2.0 ** 5.0 3.2E+1
- Negative sign
Signed Signed
number number
-(D0 + 3) -8
NOT
Logical Boolean
negation value
Boolean value NOT M0 TRUE
* Multiplication Any value Any value D0 * 3 15
/ Division Any value Any value 15 / D0 3
MOD Remainder Integer Integer D0 MOD 3 2
+ , -
Addition,
subtraction
Any value Any value D0 + 3 8
< , >,=
Comparison Any value Boolean value D0 > 2 TRUE
=,
AND, &
XOR
OR
Equal to, not
equal to
Logical AND
operation
Logical
exclusive OR
operation
Logical
inclusive OR
operation
Any value D0 2 TRUE
Boolean value
Boolean
value
M0 = TRUE FALSE
Boolean
value
Boolean value M0 & M1 FALSE
Boolean
value
Boolean
value
Boolean value M0 XOR M1 TRUE
Boolean value M0 OR M1 TRUE Lowest
*1. In the table above, the default value of M0 is FALSE, the default value of M1 is TRUE, and the default value of D0
is 5.
*2. The operands for an exponentiation operator must be constants or floating-point symbols, and must not be
devices.
11.1.5 Keyword and Comment
In computer programming, a keyword is a word which has a special meaning to the programming
language. For example, TRUE and FALSE in a program represent Boolean values, and the IF
statements in the example above represent tasks which will be executed. Besides, applied
instructions are regarded as keywords. In order to prevent a program from being compiled
incorrectly, the words which are regarded as keywords in the program can not be declared to be
symbols. However, the words which are regarded as keywords in a program can be parts of the
symbols in the program. For example, “FIFO” and “_IF” are allowed.
In a structured text, the words between (* and *) are regarded as comments. When a program is
compiled, the system automatically skips the words between (* and *) in the program. Besides, as
long as the structure of a structured text is not destroyed, comments can be put anywhere in the
structured text. However, users have to be careful about the readability of the structured text.
11-5