Function Blocks (FBs)
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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.
l
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".
For details on function blocks, refer to 6-1-5 Details on Function Blocks on page 6 - 6.
Functions (FUNs)
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Executing Function and Execution Conditions
• You can call functions from programs or other function blocks to execute them.
• Functions are always executed.
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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
input value is constant.
For details on functions, refer to 6-1-6 Details on Functions on page 6 - 10.
6-1-3
Differences between Programs, Functions, and Function Blocks
POU type
Programs Function blocks Functions
Item
Types User-defined only Instructions or user-de-
fined
Instructions only (User-
defined functions not
supported.)
Execution method Executed upon execution
of the safety task.
Called from a program or
another function block.
Called from a program or
function block.
Algo-
rithm
Any instruc-
tions
Supported. Supported. Not supported.
User-defined
function
blocks
Supported. Supported. Not supported.
6 Programming
6 - 4
NX-series Safety Control Unit User's Manual (Z930)
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