I know this question is already a bit older but:
Just in case someone else runs into this problem. If you want to enter high bytes into stdin (for example when debugging with gdb in a shell) then you first have to change the encoding of the terminal emulator you are using from UTF-8 to ISO-8859-1 or smth.something similar so your entered bytes don't get converted into smth.something else.
Once you have done this you can enter the byte values with ctrl+shift+uctrl+shift+u
and the hex number.