By the way, are you asking for what the cross connects are for the cable? If so, it is:
Code:
Skymap IIIc DB9F DB25F
2 Data Out 2 3
4 Data In (Rx Data) 3 2
5 Ground (0V or -VE) 5 7
Most laptop serial ports are DB9, but the DB25 is included for legacy units.
"Differential In" is not a standard RS-232 signal. It may be Skymap's name for Ready-To-Send (RTS) or Clear-To-Send (CTS). Both of these signals are standard RS-232 and are used for hardware handshaking signaling. They may be required, as may other cross-connected pins within the plugs.
If you're not sure about this, I'd suggest getting a cheap RS-232 analyzer. $15 at Radio Shack.