What is a NULL-Modem Cable/Adapter?
A NULL-Modem cable or adapter is designed to connect two computers that have a Male 9-pin connector designed to directly connect to a MODEM. The EIA RS232 standard has defined specific pins in these connectors to be “inputs” or “outputs”. When two computers with the same connector configuration need to be connected together directly without Modems between them, a special cable that changes the connections so that “inputs” are properly connected to “outputs” of the other computer. This special cable is called a NULL-Modem cable because it replaces the need to have two Modems between the computers. This a simple idea, but to complicate matters there are NULL-Modem “adaptors” that are only about 1″ long so that an extension cable must be added for use, and NULL-Modem cables that incorporate the extension cable. Lastly there are “partial” and “full” NULL-Modems. In all except rare circumstances, either type will work when connecting directly to a PCM.
