Using the PAUSE_REQ, PAUSED, and SINGLE STEP parameters

The operator can request a single pause by issuing a PAUSE command to the phase. This sets the PAUSE_REQ bit, indicating that the phase will pause at the next programmed transition. The phase logic resets the PAUSE_REQ bit when the next RESUME command occurs, causing only a single pause.

The SINGLE_STEP parameter indicates when the phase is in the SINGLE_STEP mode. The SINGLE STEP mode allows the phase to continue to the next programmed pause and then to wait for the operator to issue a RESUME command.

Correct operation of PAUSE_REQ, PAUSED and SINGLE_STEP depends on the phase logic to handle them appropriately. The phase logic must contain the instructions to take action on these pause commands. If no action is taken, these commands have no effect. This may be a desired behavior if, for example, pauses are not permitted.

This approach is necessary since the DeltaV Batch Executive cannot know what behavior is appropriate for all applications. The phase programmer should determine the points in the phase execution where a pause is allowed and then insert the appropriate code to deal with it. One convenient way to code this is to add a non-stored action to the SFC step as follows:

'PAUSED' = 'PAUSE_REQ'

Then, add the following logic to the transition:

NOT 'PAUSED' AND <continue your transition logic here>