If you wish to closely synchronize the sequential processing with the periodical execution of each control loop, for each loop with 2 bits contained in the status words there is:

These two bits can act as enabling conditions for processing operations written in structured text or ladder language.

This synchronization can be useful for Stop/Run operating modes, or for variation or compensation calculations.

The pre-processing status bit is on 1 during the task cycle before the control processing cycle.

The post-processing status bit is on 1 during the entire task cycle which follows the control handling cycle.

To correctly synchronize the sequential handling with the process control calculations, processing operations must be integrated within the same task.

In manual or tracking mode, the command is generated in all processing cycles. These synchronizing bits are always on 1 while in these modes.