Writes a character to a serial port.
write-serial-port-char char serial-port &optional timeout-error-p => char
A serial-port object.
write-serial-port-char writes the character char to the serial port associated with serial-port, and returns char.
A timeout will occur if the character cannot be written before the write timeout (as specified by values given when the serial port was opened by open-serial-port).
When a timeout occurs, if timeout-error-p is non-nil, then an error of type
serial-port-timeout is signaled, otherwise
nil is returned. The default value of timeout-error-p is
LispWorks User Guide and Reference Manual - 20 Sep 2017