How to enable a secondary auxiliary serial port on EXP 2 connector

This article explains how to enable and use a secondary TTL serial port on EXP2 connector

To enable the serial Port 0 of CM3+ module instead of GPIO or SPI port add this line in /boot/config.txt

dtoverlay=uart0,txd0_pin=36,rxd0_pin=37,pin_func=6

Reboot the CM3-Panel and check that the port exists by typing:

ls -al /dev/tty*

...
crw-rw---- 1 root dialout 204, 64 May 18 15:36 /dev/ttyAMA0
...

The port is available as /dev/ttyAMA0 device

The line will be

EXP2 Pin #	Signal
GPIO 36	TXD0
GPIO 37	RXD0