# Example for Acquisition

The following image shows an example PLC logic for triggering a vision system from a PLC, in this case specifically a Rockwell ControlLogix PLC:

The signals used are the following:

Signal Name | Vision System Defined Signal or Tag | PLC User Defined Tag | Notes
--- | --- | --- | ---
Online | Yes | - | Thr vision system is in online state.
TriggerEnable | Yes | - | This bit is set when the vision system is online and SetTrigEnable is set in rung 0.
TrigReq | - | Yes | You set this bit to request an image acquisition to occur in the vision system.
TrigONS | - | Yes | This bit is set to 1 program scan in the PLC after TrigReq is set to 1 and enable the rung outputs (internal bit, it is set or unset automatically by the PLC).
TriggerReady | Yes | - | The vision system is ready to accept a trigger.
TriggerAck | Yes | - | The vision system sends this acknowledgement to the PLC so it knows the trigger was accepted.
Trigger | Yes | - | Setting this bit requests an image acquisition to occur in the vision system.

In rung 0, when the vision system is online it is set to accept a trigger from the PLC by setting TriggerEnable to 1.

When you set the TrigReq bit, the Trigger bit is set if the TriggerReady bit is set and TriggerAck is not set (0). One image is acquired in the vision system for inspection. You must clear (set to 0) the TrigReq bit in order to trigger thevision system again.

If the TrigONS signal is removed from the sample logic above, then just setting the TrigReq bit causes the vision system to trigger whenever TriggerReady is set (the TriggerAck is already set to 0 from the previous trigger), and it triggers freely without needing to set or clear the TrigReq bit. Simply clearing the TrigReq bit stops the vision system from triggering and acquiring images.