Siemens SIMATIC S7-200 - Selecting between SIMATIC and IEC 1131-3 Programming Modes; Overloaded Instructions; Example of IEC Overloaded ADD Instruction

Basic Concepts for Programming an S7-200 CPU
4-15
S7-200 Programmable Controller System Manual
A5E00066097-02
Selecting Between SIMATIC and IEC 1131-3 Programming Modes
Since IEC 1131-3 is strongly data typed, and SIMATIC is not strongly data typed,
STEP 7-Micro/WIN 32 does not allow you to move programs between the two
different editing modes. You must choose a preferred editing mode.
Overloaded Instructions
Overloaded instructions support a range of data types. Strong data type checking
is still applied since all of the operand data types must match before the instruction
compiles successfully. Table 4-7 shows an example of the IEC overloaded ADD
instruction.
Table 4-7 Example of IEC Overloaded ADD Instruction
Instruction
Allowed Data Types
(Strong Data Type Checking)
Allowed Data Types
(Data Type Checking)
Compiled Instruction
ADD INT WORD, INT ADD_I (Add Integer)
ADD DINT DWORD, DINT ADD_D (Add Double Integer)
ADD REAL REAL ADD_R (Add Real)
When all of the operands have the data type DINT, an Add Double Integer
instruction will be generated by the compiler. A compilation error occurs if data
types are mixed for the overloaded instruction. What is considered illegal depends
on the level of data type checking. The following example will generate a compiler
error under strong data type checking, but will pass compile for simple data type
checking.
ADD IN1 = INT, IN2 = WORD, IN3 = INT
Strong data type checking: compile error
Data type checking: compiles to ADD_I (Add Integer)
The simple data type checking will not prevent common run-time programming
errors from occurring. With simple data type checking, the compiler will not catch
the following common programming errors: ADD 40000, 1 will be a negative
number, not an unsigned 40,001.