This command ensures that any incoming data from the specified serial port (1 for ser1, 2 for ser2) is transformed into keystrokes. Thus other computers or 8 bit keyboards can be used as an additional external keyboard. Using the command without a parameter, or zero (eg. KBD_USE 0) closes the ser channel and stops this operation.
This task is carried out in the background of any other programs, but does not actually create a job.