rawkeydown and numtochar don't work as expected

[Tiemo Hollmann TB]

Hello,

I am trying to capture a field input with rawkeydown and after doing some
other processings to regenerate the input with numtochar.

For all a-zA-Z1-0 it works fine and also for some special char, like "!,.-",
But for other input, like "?;:_" the numtochar function returns other values
as my input. All signs are lower than 255, some are lower than 127, some are
greater than 126.

Is this a matter of the charset - what I can't change - , or another thing I
forgot or am I on the wrong lane at all and it can't be done, what I want?

Thanks for your experience

Tiemo