Allen-Bradley 1756-M02AS User Manual page 124

Chapter 8 Configure Camming
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of the change and uses this information to maintain synchronization between
the profiles.
If the Execution Schedule of an instruction is set to Immediate and a position
or time cam profile is in process, the instruction errs. In this case, the
instruction generates an Illegal Dynamic Change error, error code 23, in the
programming software. This error even occurs when the axis is waiting to lock
onto the master axis.
If an Execution Schedule of Pending is selected without a corresponding
position or time cam profile in progress, the instruction executes. However, no
camming motion occurs until another instruction with a non-pending
Execution Schedule is initiated. This process allows pending cam profiles to be
preloaded before executing the initial cam. This method addresses cases where
immediate cams would finish before the pending cam could be reliably loaded.
Rockwell Automation Publication MOTION-UM002E-EN-P - June 2016