Check for uppercase? [RESOLVED]

I'm looking to write a formula that checks to see if a field uses only numbers and capital letters. It's basically making sure that the invoice number is entered correctly. Any combination of letter and numbers is ok, so long as all the letters are upper case. I see the 'uppercase' function but not sure it can do what I'm trying to accomplish. Any ideas?

Well I finally figured it out. Man this took much longer than I thought for such a simple thing, but I guess my mind works slowly :)

stringvar x;
numbervar i;
stringvar z;
numbervar strLen;
global stringvar UCaseCheck := 'Pass';

strLen := len({Command.Invoice Number});
x := totext({Command.Invoice Number});
z := totext({Command.Invoice Number});
ucase(x);

For i := 1 to strLen Do
(
Local NumberVar charPos := i;
if AscW(x[charPos]) <> AscW(z[charPos]) then UCaseCheck := 'Fail';
);

UCaseCheck;