portString: a string specifying the port to open. Under Windows, use something similar to "\\.\COM1". Under MacOS and Linux, use something similar to "/dev/*" (check the "/dev" folder to know what file to specify). Under Linux, you might have to launch V-REP with super user priviledges in order to access the serial port.
baudRate: the baudrate
reserved1: reserved for future extension. Keep at NULL.
reserved2: reserved for future extension. Keep at NULL.