The Driven Tag Group can be configured as a One-shot Tag Group. The One Shot Tag Group will not run at a rate, but instead it will be triggered by a change in the driving Tag's value. One-shot polling executes once when the condition becomes true, then waits for that condition to become false then true again. This makes it follow a 'rising edge' or 'falling edge' pattern.
Let's make a Driven One-shot Tag Group that only updates once when a Memory Tag goes to true. We are using a Memory Tag so a user can change the value when they want to poll the PLC. This is actually a good example of how an operator can ask the PLC for new values whenever they want to, using a refresh button on the screen.
Create a Memory Tag
- From Tag Browser, click on the New Tag icon or right click on a folder and select New Standard Tag > Memory Tag.
- In the Tag Editor, enter the following:
- Tag Name: One Shot Trigger
- Data Type: Boolean
- Value: false
- Click OK to add the One Shot Trigger Tag to the Tag Browser.