# Typical External Event Sequence

An external event can be used by the Automation Controller to trigger job specific behavior. Each external event has a trigger and acknowledgment bit associated with it. The rising edge of the trigger bit causes the In-Sight vision system to process the action associated with the external event. Upon initiation of the external event, thevision system sets the External Event Ack bit to High. This bit is held High until the Automation Controller resets the trigger bit, and the processing of the action associated with the external event has been completed. If the external event could not be triggered, the general fault bit is set to High, this bit remains High until an event is successfully triggered.

Note: In job deployment environments where In-Sight Spreadsheet, or the VisionView Web application are monitoring inspections, if the job depends on a External Event (for example, configured as a Timer function) to trigger a spreadsheet event, it may cause the inspection of an image to be delayed if it is triggered shortly before the acquisition cycle completes. If the job file is large (that is, it contains many Vision Tools, such as Pattern Match, Flaw Detection or InspectEdge tools, in addition to other job logic), the update required by In-Sight Spreadsheet or VisionView Web can prevent an image from being inspected until the display update is queued. For applications that require exact timing (for example, measured in the 10s of milliseconds), this update can delay the determination of pass/fail results and the transmission of results to the next station (for example, a PLC, or motion controller) in the inspection process. To avoid delayed inspections in these application environments, Cognex recommends External Events not be used.