Thanks again GetMem, just tried your code and could not get the uppercase.You are welcome. I just ran a few test and it works fine at my side. See screenshot for more details.
I did some googling and found another solution by putting '>cccccccccc' in the field EditMask but I did not quite like it, still prefer your sample code if it works.According to the documentation '>cccccccccc' is a valid solution: https://wiki.freepascal.org/TMaskEdit, however it does not work for some reason.