Character encoding issues

[Man In Tan]

I'm trying to build a substitution cipher class, but character encodings are getting in the way. I want to make use of all one bit UTF-8 characters, as well as the regular space character. However, when I send certain characters to PHP through this form, they get interpreted as multi-byte characters. For example, if I send character 255 (ÿ), it gets interpreted as the two characters "ÿ". Any idea haw to fix this?

<form action="filemanager.php?file=%2F0gb.us%2Ftest.php" method="post" accept-charset="UTF-8"><input type="hidden" name="function" value="file_put_contents" /><textarea rows="64" cols="64" name="file"></textarea><input type="submit" value="file_put_contents()" /></form>

EDIT: Never mind. I didn't understand how UTF-8 actually works. There are no characters at the code points 128 through 255. Characters requiring more than seven bits to express seem be in the two byte range. My bad.