The serial cable (also referred to as RS232) is commonly used to transfer data to and from a machine. Newer devices do not normally use serial cables as a primary data transfer method, but it is still used to communicate with older, simpler devices that are not equipped with the latest technologies.

A picture of a 9-pin RS232 serial cable

The different types of serial cables can be identified by looking at the connectors on both ends. Some have 25 pins while others only have 9. The 25-pin versions (DB25) were rarely ever utilized, so you will not see them as much as the 9-pin versions (DB9). It is not uncommon,though, to see a RS232 cable with 25 pins on one side and 9 on the other. It is also important to note whether or not the cable is wired as a null modem. Usually, a null modem RS232 cable will have “null modem” printed on the connector.

A picture of a null modem

Many people run into problems getting serial cables to work properly when connecting two computers together. When treating the connection between two machines as a network connection, a null modem must be used. The issue most people have with null modems is that they don”t realize that there are several different types of null modems to choose from. Read your requirements carefully; if a null modem is required, look for the terms “loopback” and/or”handshaking” to determine which one you need.

A null modem with cable extension