Enable UART Port on Raspberry Pi

By standard the UART interface is configured as serial console. If you want to use the UART interface for other things, e.g. for a GPS module, the standard function needs to be deactivated.

1. Open the cmdline.txt file with the Nano text editor.

   sudo nano /boot/cmdline.txt

   and remove the following part from the file.

   console=ttyAMA0,115200 kgdboc=ttyAMA0,115200

   The content of the file should look like this

   dwc_otg.lpm_enable=0 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait
   

   Exit the editor with ctrl+x and save the changes using y.

2. Open inittab

   sudo nano /etc/inittab

   and search for the following line.

   T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100

   Insert a # at the beginning of the line to comment this line. Doing so the line should look like this.

   #T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100

   Exit the editor the same ways as in the previous step.

3. From Kernel 3.18.x on the following step must be excecuted aditionally.

   sudo nano /boot/config.txt

   Search for the following line and remove the # at the beginning of the line.

   #dtparam=spi=on

   Exit the editor the same ways as in the previous step.

   Show kernel version
   uname -a
4. Restart RPI.

   sudo reboot