Lenze PLC Designer PLC Designer (R2-x) - Manual (Page 257)

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DMS 3.2 EN 02/2011 TD29 255
7.2.4 Input Variable
Between the key words VAR_INPUT and END_VAR, all variables are declared that
serve as input variables for a POU. That means that at the call position, the value of
the variables can be given along with a call.
Example:
VAR_INPUT
iIn1:INT (* 1. Inputvariable*)
END_VAR
7.2.5 Output Variable
Between the key words VAR_OUTPUT and END_VAR, all variables are declared that
serve as output variables of a POU. That means that these values are carried back to
the POU making the call. There they can be answered and used further.
Example:
VAR_OUTPUT
iOut1:INT; (* 1. Outputvariable*)
END_VAR
7.2.6 Input and Output Variables
Between the key words VAR_IN_OUT and END_VAR, all variables are declared that
serve as input and output variables for a POU.

Stop!
With this variable, the value of the transferred variable is changed ("transferred as a
pointer", Call-by-Reference). That means that the input value for such variables
cannot be a constant. For this reason, even the VAR_IN_OUT variables of a function
block can not be read or written directly from outside via
<functionblockinstance><in/outputvariable>.
Example:
VAR_IN_OUT
iInOut1:INT; (* 1. Inputoutputvariable *)
END_VAR