Overview Of The Three Types Of Pous - Omron NX-SID Series User Manual

7 Programming
7-1-2

Overview of the Three Types of POUs

Programs
 Executing Programs and Execution Conditions
• You execute a safety task to execute the programs that are assigned to that safety task.
• Programs are always executed.
 Notation
• The POUs must include at least one program. More than one program can be assigned to the
safety task.
Function Blocks (FBs)
 Executing Function Blocks and Execution Conditions
• You can call function blocks from programs or other function blocks to execute them.
• Function blocks are always executed.
• To execute a function block for only specific conditions, pass a TRUE value to the Activate input
variable of that function block. The function block is not executed if the value of the Activate input
variable is FALSE.
 Notation
• There are both user-defined function blocks and system-defined function blocks.
User-defined function blocks are sometimes called user-defined FBs. System-defined function
blocks are sometimes called FB instructions.
Refer to 7-1-5 Details on Function Blocks on page 7-6 for details on function blocks.
Functions
 Executing Functions and Execution Conditions
• You can call functions from programs or function blocks to execute them.
• Functions are always executed.
 Notation
• You cannot create user-defined functions.
• System-defined functions are sometimes called FUN instructions.
• The values of internal variables are not retained. The output value remains constant as long as
the input value is constant.
Refer to 7-1-6 Details on Functions on page 7-10 for details on functions.
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NX-series Safety Control Unit User's Manual (Z930)