This link has some value. smile

Note that (as we have seen) Pins 2 and 3 are the main ones of interest, and:-

Quote:
In current usage, the term "RS-232" is often used to mean "ASCII (or ANSI) serial protocol", and no longer indicates specific voltage levels. For a serial link, care should be taken that the signal voltages at the two ends of the link are compatible. For example, a PC COM port operating at a nominal 12 volts is incompatible with the serial connector of a microprocessor platform operating at 3 volts.

If you don't inspect ... don't expect.