The function get-serial-port-state
queries various aspects of the state of the serial port associated with serial-port.
The argument keys should be a list of one or more of the keywords :dsr
and :cts
. These cause get-serial-port-state to check the DSR and CTS lines respectively.
The result state is a list giving the state of each line in the same order as they appear in the argument keys.
LispWorks User Guide and Reference Manual - 20 Sep 2017