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Section 2 Programming Languages
2-4 ST Language
The ST language consists of operators and statements. Operators perform basic operations such as arithmetic or comparison
operations. Statements specify the sequence of program execution and the flow of program control. ST language is a structured
text language that is composed of a combination of these operators and statements.
Statement
<Examples of ST language>
Statement
Conditional expression
A conditional expression
consists of variables,
an operator (e.g., >),
and immediate values.
Executable statement
An executable statement
consists of variables,
operators, and an
assignment statement.
A control statement, which is made up of
statements, conditional expressions, and
executable statements, is terminated by
a semicolon (“;”).
Comment
A comment begins with “(*”and ends with“*).”
No. Operation
Operator
Data type
Description
Sample value Precedence
1
Parentheses
(expression)
(2+3)*(4+5)
45
Highest
2
Function
Function name
(parameter)
LN(A)
MAX(X, Y)
3
Exponentiation
**
REAL (base, exponent)
3.0**4.0
8.1E+1
4
Sign inversion
-
INT, DINT, REAL
-Voo1 (Voo1=10)
-10
5
Logical not
NOT
BOOL, WORD, DWORD
Logical NOT of
each list
FALSE
6
Multiplication
*
INT, DINT, UINT, UDINT, REAL 10*3
30
7
Division
/
INT, DINT, UINT, UDINT, REAL 6/2
3
8
Division remainder MOD
INT, DINT, UINT, UDINT
17 MOD 10
7
9
Addition
+
INT, DINT, UINT, UDINT, REAL 2+3
5
10 Subtraction
-
INT, DINT, UINT, UDINT, REAL 4-2
2
11 Comparison
<, >, <=, >=
Elementary
(excluding STRING type)
4>12
FALSE
12 Equality
=
Elementary
(excluding STRING type)
T#26h =T#1d2h
TRUE
13 Inequality
<>
Elementary
(excluding STRING type)
8<>16
TRUE
14 Logical product
&, AND
BOOL, WORD, DWORD
TRUE & FALSE
FALSE
15 Exclusive or
XOR
BOOL, WORD, DWORD
TRUE XOR FALSE TRUE
16 Logical add
OR
BOOL, WORD, DWORD
TRUE OR FALSE
TRUE
Lowest
* Statements, conditional expressions, and executable statements must be separated by at least one space character.
2-4-1 ST operators
