Knowledge Base / Rockwell In-chassis / ControlLogix / MVI56E Series / MVI56E-MNETC

What causes a conditional command to be issued?

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A conditional command is useful when the same value does not need to be written to the end device continuously, but rather on change. 

A conditional write command is scanned based upon its poll rate (like all other commands).  The difference is that it will not be executed unless any of the write data associated with the command has changed.  For example, if the starting address is 0, and the count is 10 for the command, if any value within registers 0 - 9 changes, the command will be issued.

The command will be issued once when a change in data is detected, unless a failure occurs.  If a failure occurs than it will retry according to the retry count parameter configuration.