Using the serial port on the RaspberryPi

there are several minor things in the way if you want to have dedicated control of the serial port on a raspberry pi

the first is kernel boot messages at startup, those are caused by the kernel parameter console=ttyAMA0,115200 set in /boot/cmdline.txt

next is the login prompt, set in /etc/inittab with the line T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100

kernel debuging is also on the serial port and i dont know what effect it may have on the end-use, so you may want to turn that off also in cmdline.txt, just remove kgdboc=ttyAMA0,115200

once all of those are off, you can use /dev/ttyAMA0 like any normal linux serial port, and you wont get any unwanted traffic confusing the attached devices