Text entry box character limit

I need to set a text entry so that it accepts only two characters. This happens on any text entry box. If you continue to type the text just scrolls to the left into oblivian. I've tried doing this by making the text entry box small (two characters wide) but that doesn't work. If the user types in more than two characters the characters just scroll to the left and you can input an endless amount of characters. I don't think there is a way to set a limit on the number of characters in a text entry so is there some kind of trick?

Thanks.