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Will saving changes to a Functional Block program cause outputs to cycle?


When making modifications to a Functional Block program will this result in outputs cycling?


Enterprise Server

Automation Server

Functional Block


Functional Block programs operate by sending the signal of each block to the next connected block each program cycle. The functional block program also stores in its memory the last value of the block when committing a change and restarting the program. Due to the memory of the block values outputs of the Functional block program should normally avoid fluctuation when saving to the database.

Situations where value will be held

  • No change to logic impacting this output in save to program and Delay blocks are not used

Situations where value can fluctuate

  • Change to logic that directly impacts the output signal
  • Use of Delay blocks in control logic for output

The delay block will reset to the specified default value when you save the application and if this used in the control logic for your output it can result in a one program cycle fluctuation in the output value.


To avoid any physical device damage when saving a change to the Functional Block program it is recommended to be cautious and use overrides while the program change is occurring. This can be done in software by forcing an output value (on IO module) or using Hand/Auto/Off (HAO) controllers on the output device.

Use of these overrides will protect your physical equipment and allow you to validate the programming logic changes after saving.

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Last update:
‎2018-09-06 10:41 AM
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