Omega Vehicle Security 1400 manual Trigger and Stop Events, Post-Trigger State, Post-Stop State

Appendix B Configuration Aspects for Programmers

Post-Trigger State

The Post-Trigger state is the period between the occurrence of the trigger event and the occurrence of the stop event. While the unit is in this state the TRIGGER LED will be on and the alarms and their associated outputs will be updated at the post-trigger scan rate.

During the Post-Trigger state the unit will collect Post-Trigger data at the rate specified by the acquisition scan interval specified by the Scan Interval (I) command. Post-Trigger scans will be collected at this rate until the stop event occurs. The number of scans collected during the Post-Trigger state is not restricted by the internal buffer size. ChartScan can collect scans in the post-trigger state indefinitely if the controlling computer is capable of reading data out of the acquisition buffer fast enough to prevent a buffer overrun.

The Post-Trigger state may be detected by querying the Triggered Bit of the Status Byte (STB) Register and the Stopped Bit of the Event Status Register (ESR). ChartScan is in the Post-Trigger state if and only if the Triggered Bit of the STB is set and the Stopped Bit of the ESR is not set. The unit will exit the Post-Trigger state when the stop event occurs.

Post-Stop State

The Post-Stop state is the period between the occurrence of the stop event and the completion of the acquisition. While the unit is in this state the TRIGGER LED will be on and the alarms and their associated outputs will be updated at the post-stop scan rate.

ChartScan will only enter this state when a non-zero value of the post-stop count parameter of the Set Counts (Y) command has been specified. If this is the case, upon the occurrence of the stop event the unit will enter the Post-Stop state and collect the specified number of post-stop scans.

When the specified number of post-stop scans have been collected, the unit will terminate the current acquisition and return to a non-acquiring state. If, however, the post-stop count parameter of the Set Counts (Y) command is zero the unit will return immediately to a non-acquiring state upon the occurrence of the stop event (unless the Auto-Rearm feature is used).

The Post-Stop state may be detected by querying the Stopped and the Acquisition Complete bits of the Event Status Register (ESR). ChartScan is in the Post-Stop state if and only if the Stopped Bit of the ESR is set and the Acquisition Complete Bit of the ESR is not set. The unit will exit the Post-Stop state when the specified number of post-stop scans have been collected. When this occurs the Acquisition Complete Bit of the ESR will be set and the unit will return to a non-acquiring state (unless the Auto-Rearm feature is used).

Trigger and Stop Events

The programmed system events are the driving force behind any acquisition. The trigger point (also referred to trigger event) signals the end of the pre-trigger and the beginning of the post-trigger; the stop event signals the end of the post-trigger and the beginning of the post-stop.

In addition to the pre-trigger (normal) scan interval, a secondary post-trigger (acquisition) scan interval can be assigned. This would allow scans during the post-trigger and post-stop states to be collected faster or slower than those in the pre-trigger. One application for this secondary scan interval is when events after the trigger require faster sampling than those before the trigger, such as during alarm conditions.

ChartScan can be configured to start data acquisition on one of many trigger sources. The Trigger Configuration (T) command is used to set: the source of the trigger (GET, Talk, etc.), the trigger start and stop event, a pre-trigger count and/or post-stop count if used, the direction of the trigger source level if used (rising or falling edge), and whether the Auto-Rearm flag is enabled.

If the Auto-Rearm feature is in use, the unit will immediately begin looking for another trigger event once a stop event and post-stop event is detected. If the feature is not in use, a T command must be issued after a stop event before the unit can begin looking for a trigger. However, using Auto-Rearm does not allow the user to change the trigger configuration between triggers; the initial configuration will be used until Auto-Rearm is disabled. To disable Auto-Rearm, a T command must be issued with the flag set to zero. Data will still be available after the T command is issued. Refer to the Command Reference section for details.

ChartScan User’s Manual B-13