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7 Programming
NX-series Safety Control Unit User’s Manual (Z930)
7-1 POUs (Program Organization Units)
7
7-1-1 What Are POUs?
7-1 POUs (Program Organization Units)
The safety program that runs on a Safety CPU Unit is made from a combination of POUs (program
organization units).
This section describes the configuration and specifications of POUs.
Refer to 7-5 Programming Operations on page 7-27 for the procedures to create POUs on the Sysmac
Studio.
Refer to the Sysmac Studio Version 1 Operation Manual (Cat. No. W504) for the procedures to create
POUs that are used with an NJ/NX-series CPU Unit.
A POU (program organization unit) is a unit that is defined in the IEC 61131-3 user program execution
model. A POU includes a local variable table and an algorithm (i.e., a series of code or logic). It is the
basic unit used to build the safety program.
You combine POUs to build a complete safety program.
There are three types of POUs, as described below.
Programs
A program corresponds to a main routine. It is the main type of POU that is used for algorithms. You
can place any instruction, function, or function block in the algorithm of a program.
Function Blocks (FBs)
A function block can output different values even with the same inputs. Function blocks are exe-
cuted when they are called from a program or another function block.
Functions (FUNs)
A function always outputs the same values for the same inputs. Functions are executed when they
are called from a program, another function, or a function block.
The POUs consist of a combination of these three types of POUs. You can create many POUs. You
assign the safety programs to a safety task to execute them. Only one safety task can be used by the
Safety CPU Unit.
7-1-1 What Are POUs?
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