You may hate tip and love kermit or pcomm. I understand. But, do this next procedure via tip to keep it simple, OK?
Decide which serial port you want to use. (One with no cable already plugged in is often a good bet.) The port will be labeled A, B, A/B or could even be C or higher.
If you use one labeled A/B and have no Y-type splitter cable plugged into it, you'll have access only to port A. With the splitter, you'll get ports A and B on separate sockets f the splitter cable. The pinout of the splitter cable can be found at the following URL.
The Sun serial port device driver splits each physical port into two logical devices, /dev/term/a or /dev/term/b ...