For recent 30 years we have seen great progress in electronics, and the manufacturers accepted the simplified versions of RS-232-C interface for usage in such spheres which couldn't be imagined in sixties. Today practically all modern serial interfaces comply to RS-232-C standard in signal voltages, protocols and pins. As none of the simplified variants was accepted as a standard, though many standards were created with minor cable and protocol changes, all of them are compatible with any RS-232-C standard socket but incompatible with each other. Most problems you'll face connecting RS-232-C interface are listed below:

• absence or loss of data flow control signals (connection confirmation) which leads to buffers overflow or connection abortion;
• incorrect connection when using cables (DTE and DCE), it mainly leads to incorrect connection of receiving and transmitting lines, though any other control signals can be connected incorrectly;
• incorrect configuration of the socket type or pins position, that impedes the connection according to the circuit.

Luckily enough the circuit of RS-232-C standard device provides great stability of work when the signals connection is incorrect, including ground connection or connection of two signals from one device. In any case if the serial interface between two devices works incorrectly, disconnect the cable connecting the devices until the trouble is eliminated.