The SER built-in module is an interface between the Python core and the device serial port over the RXD/TXD pins direct handling. You need to use the SER built-in module if you want to send data from the Python script to the serial port USIF0 and to receive data from the serial port USIF0 to the Python script. This serial port handling module can be used, for example, to interface the module with an external device (such as a GPS) and read/send its data (e.g. NMEA). If flow control is not enabled (default) the SER built-in module will also allow to control physical lines used as GPIO. If flow control is enabled, only available from version 12.00.xx4, version 13.00.xx5 and version 18.11.004, it will not be possible to control physical lines used as GPIO.
If you want to use SER built-in module you need to import it:
import SER
then you can use its methods, like in the following example:
a = SER.set_speed('9600')
b = SER.send('test')
c = SER.sendbyte(0x0d)
d = SER.read()
which sends 'test' followed by <CR> and receives data.
More details about SER built-in module methods can be found in the following paragraphs.