Is the Pincode field in a Web application or a Windows application? If it is a Web Application can you send a copy of the actual HTML element, you can get this from the OuterHtml property when in interrogation and the field is created and matched.
Can you clarify what you are trying to do? Are you trying to trigger this activity from a Pega app using RDA and then return the result to Pega? If not, what exactly are you trying to accomplish? The answer to your question will be based on what you are trying to do.
There is a method, RaiseEvent, available on Web Controls. This method can be used to raise various events on the control to trigger an action. It is hard to speculate which event will trigger the update, you will have to experiment trying several of the events. It may take a combination of event. The most used events for this try of requirement are; onBlur, onKeyUp, onKeyDown, onKeyPress. You might be able to determine which events are needed by looking at the actual HTML element of the text box control you are working with.