Understanding DCE & DTE connections

All RS232 devices that use a DB-9 connector should conform to the standard TIA/EIA-574. The device should be either DCE or DTE. DCE devices should have a female DB-9 connector, and DTE devices should have a male DB-9 connector. For a description of pin outs for the RS232 DB-9 connector see attached document "PinoutStndrds.pdf" from Cisco (page 2). Any RS232 device that has a DB-9 connector and conforms to this standard will connect easily to the Digi PKG-R (PKGR) or development kit radio modems.

These guidelines can help in understanding the terminology:

  • RS232 COM ports are normally configured as either a DTE (Data Terminal Equipment) port or a DCE (Data Communications Equipment) port.
  • The COM port on a personal computer is a DTE port (male).
  • The COM port on Digi radio modems are configured as DCE port (female).
  • Any device that connects to a computer COM port using a straight through serial cable is a DCE device.
  • Connect a DCE device to another DCE device using a null modem (male-to-male) adaptor.
  • Connect a DTE device to another DTE device using a null modem (female-to-female) adaptor.
  • Replace a straight through serial cable with RF modems according to the diagram below:


Last updated: Aug 23, 2017

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