ShowPlay Reference Manual, Chapter 4 (StimulusEvents): writeport
usage: writeport id flg start duration value portnum
The WRITEPORT stimulus event causes a value to be sent to an external data port at the time specified by the START argument. The DURATION argument can be used to indicate a time delay until the next stimulus, but the DURATION has no meaning for the WRITEPORT operation itself. If the output port is a digital port, the value written will remain active on that port until a new value is written.
The PORTNUM argument specifies which data port will be writtten. CIGAL specifies external ports as:
PORTNUM: -1 - digital port 100 - printer port 1 - COM1 serial port 2 - COM2 serial port 3 - COM3 serial port ...