Length of the screen field

Hi,

I am doing module pool programming, I have defined a field as pxxxx-currency(length 13) as an I/O . But on the screen painter I reduced the field length to 8 characters and so when I execute its taking 8 characters only as input but I want the field to take 13 characters I mean as we type it should take take in the whole 13 and I really do not care if it hides the first or the last characters and I cannot increase the field lenght because of the size restricitons as I have already maxed out with the screen width. All suggetions are appreciated and suitable rewarded.

Regards

Vick