What is the difference between an RS232 DTE and DCE port?How can I tell what kind of port my serial device has?What are examples of equipment that has a DTE port?What are examples of equipment that has a DCE port?

The RS232 spec references two kinds of device, DTE (Data Terminal Equipment) and DCE (Data Computing Equipment).Click here for detailed information on the differences between these two kinds of connectors.

Here are some helpful guidelines to tell them apart:

1) On DB serial connectors check if pin 2 is an input or an output. There are different rules for DB25s and DB9s.

DB25:

If pin 2 is labeled TX and is an OUTPUT the connector is DTE

If pin 2 is labeled TX and is an INPUT the connector is DCE

DB9*:

If pin 2 is labeled RX and is an INPUT the connector is a DTE

If pin 2 is labeled RX and is an OUTPUT the connector is a DCE

This is helpful in most cases, but it is a de-facto standard and may not always apply.

2) A rule of thumb for DB9 and DB25 connectors is: If it's male it is likely to be a DTE, if it's female it's likely to be a DCE.

This is a good place to start if you have no documentation on the serial device. There are many cases where this does not apply, for instance most serial printers have a female DB25 connector, but they are DTEs.

The only way to find out for sure what kind of connector a particular serial device has is to check it's documentation or contact it's manufacturer and ask.

In the worst case you may need to put a breakout box between the Lantronix product and the serial device and manually swap connections between pins until you find a connection that works. See the FAQs at the links below for information on common cable configurations.

Examples of products that usually have DTE ports are terminals, printers and the COM ports on a PC.

An example of a product that usually has a DCE port is a modem.

For more detailed information on RS232 serial wiring please click here.

For cabling information for most Lantronix products with RJ45 serial ports click here.

*Note: For decades a 9 pin D-subminiature connector has been referred to as a DB9. Recently there has been a movement to use the more accurate DE9 designation. For consistency in our documentation, and to avoid confusion, Lantronix will continue to use the term DB9 to describe a 9-pin D-subminiature serial port for the forseeable future.

For more infomation on why DE9 is considered to be more accurate see:
http://en.wikipedia.org/wiki/D-subminiature

[Originally Published On: 03/29/2006 03:09 PM]