Chapter 3 Program Organization Units - Mitsubishi Electric MELSEC iQ-R Series Programming Manual

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PROGRAM ORGANIZATION UNITS
There are three types of program organization units (POUs).
• Program block
• Function
• Function block
Processing can be described in the programming language that suits the control performed in each POU. Processing can be
described in the ladder diagram, structured text language, or FBD/LD in a function or a function block.
Functions and function blocks are called and executed by program blocks.
Project
Program file
POU
POU folder
POU POU
POU
A structured program is a program created by components. Processes in lower levels of hierarchical
sequence program are divided into several components according to their processing information and
functions.
Each component of a program is specified to have a high degree of independence for easy addition and
replacement.
The following are the examples of processing that would be ideal to be structured.
• Processing which is used repeatedly in a program
• Processing which can be separated as one function
This chapter describes two types of POUs using labels.
Devices can also be used in the program (worksheet) of each POU. For details on devices, refer to the following.
 MELSEC iQ-R CPU Module User's Manual (Application)
Up to 32 worksheets can be created in one POU in the structured text language and FBD/LD.
Set the execution order of multiple worksheets on the "Worksheet Execution Order Setting" window of the
engineering tool. ( GX Works3 Operating Manual)
Used
Program block
Function block
Function
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