RS232 Serial Data Cables and Pin Connections

- details of RS232 serial data cables and their pin connections for both 9 way and 25 way connectors and diagrams of cables for RS232.

RS232 tutorial includes:

    •  RS232 tutorial
    •  EIA & RS232 standards
    •  RS232 Handshaking
    •  RS232 signals and voltage levels
    •  RS232 pinouts
    •  RS232 loopback
    •  RS232 serial data cables

RS232 serial data cables are commonly used in data networking applications. These data cables are required to connect two RS232 devices together. Fortunately not all the signals provided within RS232 need to be implemented in a practical RS232 data cable. As a result, designs for a variety of serial data cables may be seen on the Internet and elsewhere.

In addition to this, further confusion is caused by the fact that RS232 was designed to connect modems and terminal devices or teleprinters so that telephone lines could be used to transit data over the telephone system, and serial data cables were required to connect the equipment at the remote end. This intended application for RS232 gives rise to the terminology associated with these serial data connections, i.e. DCE (Data Communications Equipment or Modem) and the DTE (Data Terminal Equipment or teleprinter).

Although many manufacturers agree on the general application of the types of RS232 serial data cables, there is still confusion in many quarters over what may be required. As a result it is always best to be aware of the complications that exist. As a result it may often be necessary to experiment a little.

Serial data cable basics

Pins are assigned within the DTE and DCE such that a "1:1" cable should be used, i.e. on where pin number X at one end is connected to pin number X at the other end and there are no crossovers.

Thus a DTE transmits data on pin 2 and the DCE receivers data on pin 2. Similarly The DTE receives data on pin 3, whereas the DCE transmits on pin 2.

Adopting this approach makes the construction of RS232 serial data cables much easier. It also saves considerable complications by not having to work out which wires to cross over in the serial data cable.

Complications do arise when cables are required to connect two items both configured as the same form of equipment, i.e. both a DTE or both a DCE.

Serial data cable diagrams and pin connections

Different data systems utilise different levels of handshaking when using RS232. Some of the simpler systems just send the data without any hard wired handshaking and as a result the serial data cables required for this are very simple. These systems may utilise the use of software codes such as X-ON / X-OFF, ACK, NAK, etc to provide the handshaking that is required. These systems require serial data cables that incorporate the transmit and receive data lines as well as an earth line. A suitable cable is shown below.

RS232 serial data cable using minimum number of connections

More comprehensive systems may utilise the additional lines provided by RS232. According serial data cables for these systems require the additional lines to be incorporated into the serial data cables for them to operate correctly. A suitable cable is shown below.

Typical RS232 serial data cable

While it is possible to buy RS232 serial data cables, it is also easy to manufacture them if the relevant connectors are available. If there are no complications, i.e. they are wires as for a DTE to DCE connection, a serial data cable will simply require one to one connections of the required pins.

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