TTY without echos

[Shawn Hayes]

     I'm trying to set up a program to read and write characters to a tty
port.  What I would like to have happen is I read a character from the port
and if it's a numeric character I echo it back, and if it is anything else
I ignore it.  Currently I can type in alphabetic characters and they are ignored
, but as soon as I echo a numeric character back to the terminal the port
echoes every character. 

   I've set up the port with a  stty -echo -echoe -echok raw
but something must still be wrong in the setup.  Is there a way to configure
a tty port to never echo characters, so that only the output from my program
shows up on the port?

                                                         Shawn Hayes