nRF9160 serial communication with UART


I want to send and receive data over UART from an external microcontroller, but without using the VCOM ports. The main goal is to send sensor data from an external microcontroller to the nRF9160 DK and then use the MQTT protocol to publish the data. In my project i can only connect the nRF9160 to a power supply with a flashed program, so it wont be connected to a computer. 

So far, i have only managed to route the UART port to the Arduino I/O pins, but this is trough the VCOM port. I have tried the method described in the link, but it dosent seem to work.

Is there a way of using UART without being connected to a VCOM port? 

Kind Regards,