<4. Control Application Creation>
4.6.2 Procedure for Creating a POU
This section describes the procedure for creating a POU using as example the logic
for detecting a mode, status or alarm condition of an NPAS POU given in Section
9.2.2, “How to Detect Mode, Status and Alarm” of Chapter 9, “Advanced
Engineering.”
● Selecting Usage for Variables of a POU
When creating a POU, the property of a variable its usage can be selected. The five
available usage options are VAR, VAR_EXTERNAL, VAR_INPUT, VAR_OUTPUT
and VAR_IN_OUT. Among these, VAR and VAR_EXTERNAL are similar with
general programming languages.
VAR_INPUT : External data to be read into a POU
Besides global variables, data of VAR_INPUT type are
read and used for calculation within a POU.
VAR_OUTPUT : Output data from a POU
Select VAR_OUTPUT type for outputting internal
calculation results of a POU.
VAR_IN_OUT :Select VAR_IN_OUT type for external data to be read into
a POU, overwritten and then re-output from the POU.
When creating a POU, in addition to VAR and VAR_EXTERNAL, VAR_INPUT,
VAR_OUTPUT and VAR_IN_OUT can be used.
● Procedure for Creating a POU
Create the control logic shown in the figure below as a POU.
1. Register a POU
1.1 Right-click on [Logical POUs] in Logic Designer, and then select [Insert]-
[Function Block] from the pop-up menus.
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