The 34540 is used with communications from SunSaver MPPT (or other Morningstar products) to the data logger or PC. When you are using the 34540 with a CR6 or CR1000X datalogger, you must also use pn 31055. When you are using the 34540 with a CR300 or CR310 datalogger, use a null modem cable as well, such as pn 18663.
The 34540 converts a controller's meter port (RJ-11 phone-type connector) to a standard RS-232 serial connector for connection to a PC or other equipment. The 34540 can be used with any Morningstar controller or inverter that is equipped with a meter connection but does not already have an RS-232 port.