Hello Jinyistudio. The command "stty" is specific for Linux. You must have the "root" rights to use it. As I wrote at the beginning of this thread, I'm using a very old tablet based on Android 2.2 with heavy firmware modifications (Uberoid image + modifications of init.rc). Starting from Android 1.6 (my first tablet) going to Android 4.4 the Google OS suppressed many Linux commands. For serial ports, a "modern" approach will be the USB-Serial library; using this library you can control an external USB-to-serial interface without the need of "stty" for the baud rate, num. of bits, parity etc. Anyway, just to try what works and what doesn't, you can use an App called "terminal emulator" and play with the available Linux commands.