Overview Of The Three Types Of Pous - Omron NJ-series User Manual

6 Programming
6-2-2

Overview of the Three Types of POUs

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Programs
 Executing Programs and Execution Conditions
• You execute a task to execute the programs that are assigned to that task.
• Programs are always executed.
 Notation
• The POUs must include at least one program. You can assign up to 128 programs to a single 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.
• If you want a function block to execute only when a condition is met, you must define an input vari-
able that sets the execution condition.
 Notation
• You can use any instruction, user-defined function, or user-defined function block in the algorithm
of a function block.
• You can retain the values of internal variables. Therefore, you can retain status, such as for timers
and counters.
• There are both user-defined and system-defined function blocks.
User-defined function blocks are called user-defined function blocks. System-defined function
blocks are sometimes called FB instructions.
For details on function blocks, refer to 6-2-5 Details on Function Blocks.
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Functions
 Executing Functions and Execution Conditions
• You can call functions from programs, other functions, or function blocks to execute them.
• The EN input variable specifies the execution condition. A function is executed only once each
time EN changes to TRUE.
 Notation
• You cannot use FB instructions or user-defined function blocks in algorithms.
• The values of internal variables are not retained. Therefore, the output value remains constant.
• There are both user-defined and system-defined function blocks.
User-defined functions are called user-defined functions. System-defined functions are some-
times called FUN instructions.
For details on functions, refer to 6-2-6 Details on Functions.
6-6 NJ-series CPU Unit Software User's Manual (W501)