Triggering an action off of an input text field without using a button

I have an input text field set to Password and set to a max of 8 characters. When the 8 characters have been typed in to the input field this needs to trigger (without any sort of button action involved) the playhead moving to frame 20 of the timeline.

I have labeled my input field as passwordTxt.

Any ideas on the AS 2.0 code to make this work? Thank you.