Siemens S7-1200 - Page 183

Programming concepts
6.5 Programming language
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG
183
Constructing an SCL expression
An SCL expression is a formula for calculating a value. The expression consists of operands
and operators (such as *, /, + or -). The operands can be tags, constants, or expressions.
The evaluation of the expression occurs in a certain order, which is defined by the following
factors:
● Every operator has a pre-defined priority, with the highest-priority operation performed
first.
● For operators with equal priority, the operators are processed in a left-to-right sequence.
● You use parentheses to designate a series of operators to be evaluated together.
The result of an expression can be used either for assigning a value to a tag used by your
program, as a condition to be used by a control statement, or as parameters for another SCL
instruction or for calling a code block.
Table 6- 2 Operators in SCL
Type
Operation
Operator
Priority
Parentheses
( Expression )
( , )
1
Math
Power
**
2
Sign (unary plus)
+
3
Sign (unary minus)
-
3
Multiplication
*
4
Division
/
4
Modulo
MOD
4
Addition
+
5
Subtraction
-
5
Comparison
Less than
<
6
Less than or equal to
<=
6
Greater than
>
6
Greater than or equal to
>=
6
Equal to
=
7
Not equal to
<>
7
Bit logic
Negation (unary)
NOT
3
AND logic operation AND or & 8
Exclusive OR logic operation
XOR
9
OR logic operation OR 10
Assignment
Assignment
:=
11
As a high-level programming language, SCL uses standard statements for basic tasks:
● Assignment statement: :=
● Mathematical functions: +, -, *, and /
● Addressing of global variables (tags): "<tag name>" (Tag name or data block name
enclosed in double quotes)
● Addressing of local variables: #<variable name> (Variable name preceded by "#" symbol)