Passing Parameters To Blocks - Siemens SIMATIC S7-1200 System Manual

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Passing parameters to blocks

Function Blocks (FB) and Functions (FC) have three different interface types:

FBs and FCs receive parameters through the IN and IN/OUT interface types. The blocks

process the parameters and return values to the caller through the IN/OUT and OUT

interface types.

The user program transfers parameters using one of two methods.

Call-by-value

When the user program passes a parameter to a function as "call-by-value", the user

program copies the actual parameter value into the input parameter of the block for the IN

interface type. This operation requires additional memory for the copied value.

When the user program calls the block, it copies the values.

Call-by-reference

When the user program passes a parameter to a function as "call-by-reference", the user

program references the address of the actual parameter for the IN/OUT interface type and

does not copy the value. This operation does not require additional memory.

When the user program calls the block, it references the address of the actual parameters.

Generally, use the IN/OUT interface type for structured tags (for example, ARRAY,

STRUCT, and STRING) in order to avoid increasing the required data memory

unnecessarily.

S7-1200 Programmable controller

System Manual, V4.2, 09/2016, A5E02486680-AK

Programming concepts

7.3 Using blocks to structure your program