Lenze PLC Designer PLC Designer (R3-1) - Manual (Page 75)

L-force | PLC Designer
Concepts and Base Components

DMS 4.1 EN 03/2011 TD29 73
Function Block Instance
Function blocks are always called through an instance which is a reproduction (copy) of
a function block.
Each instance has its own identifier (instance name), and a data structure containing
its inputs, outputs, and internal variables.
Instances like variables are declared locally or globally, whereby the name of the
function block is indicated as the data type of an identifier.
Syntax for declaring a function block instance:
:;
Example
Declaration (e.g. in the declaration part of a program) of instance INSTANCE of
function block FUB:
INSTANCE: FUB;
The declaration parts of function blocks and programs can contain instance
declarations. But: Instance declarations are not permitted in functions.
Calling a function block
Function blocks are always called through a function block instance. Thus a function
block instance must be declared locally or globally.
Then the desired function block variable can be accessed using the following syntax:
Syntax:
.
Regard the following:
• Only the input and output variables of a function block can be accessed from
outside of an function block instance, not its internal variables.
• Access to a function block instance is limited to the POU in which it was declared
unless it was declared globally.
• At calling the instance the desired values can be assigned to the function block
parameters. See below.
• Please regard, that the InOutVariables (VAR_IN_OUT) of a function block are
passed as pointers.
• In SFC function block calls can only take place in steps.
• The instance name of a function block instance can be used as an input parameter
for a function or another function block.
• All values of a function block are retained until the next processing of the function
block. Therefore function block calls do not always return the same output values,
even if done with identic arguments!
Note: If there at least one of the function block variables is a
remanent
variable, the
total instance is stored in the retain data area.