# Operation

An External Event can be used by the PLC to trigger job specific behavior. Each External Event has an event trigger and acknowledgment bit associated with it. The rising edge of the External Event trigger bit causes the vision system to process the action associated (running tools, cells, etc) with the External Event. Upon initiation of the External Event, the vision system sets the External Event Ack bit to 1. This bit stays set to 1 until the PLC resets the External Event trigger bit to 0. If the external event could not be triggered, the Error bit is set to 1.

Note: In job deployment environments where In-Sight Vision Suite or the WebHMI are monitoring inspections, if the job depends on an External Event 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 Vison Suite or the WebHMI may 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 or fail results and the transmission of results to the PLC in the inspection process. To avoid delayed inspections in these application environments you need to take care to ensure that if External Events are triggered while a machine is running, that the cells triggered by that External Event run quickly. Actions like resetting counters or latching small cells are okay, but triggering a training or another set of tools can cause delays in getting results.