Alex,
It depends on whether the device is DCE (Data Communications Equipment)
or DTE (Data Terminal Equipment). Modems are DCE and Computers are DTE (as a
general statement). Pin2 is DTE Transmit data (TDX) and is an output from a
DTE device and an input to a DCE device. Pin2 is DTE Receive data (RDX) and is
a DTE input line and a DCE output line. That's why a NULL modem cable has
these reversed…it takes the "output" from one computer and attaches it to the
"input" of the other computer…and vice versa.
Don