UART (Universal Asynchronous Receiver/Transmitter) is an individual (or part of an) integrated circuit used for serial communications over a computer or peripheral device serial port. It is commonly used in conjunction with communication standards such as RS-232, RS-422 or RS-485.
Refer these articles for more information about Serial ports available on Colibri modules:
On Evaluation Board v3.1A: Connect one end of the null modem cable to the serial port of the PC and the other end to upper RS232 port on connector X25.
On Iris board V1.1A: Connect one end of the null modem cable to the serial port of the PC and the other end of null modem cable to connector X14.
Use a terminal application, such as Tera Term to open a terminal connection on the PC with these settings: 9600 Baud/ 8 Data Bits/ No parity/ 1 Stop Bit.
This application demonstrates how to read and write data using CoM port.
Open a Tera Term window (on PC) and start a new Serial connection with the following settings:
Send message from PC (work station) and you will see the number of bytes in buffer, press Read button to read message received from PC (work station).