Abstract: A network data processing system has a port that can be configured for any one of plural data formats, for example, for ATM or Frame Relay. The port configuration can be accomplished without re-manufacturing the network data processing system. The configuration can be accomplished by signals on external pins of integrated circuits forming the network processing system, and/or by software. In some embodiments, the port can be configured for any one of plural interfaces used for connection to physical layer devices, for example, UTOPIA or the serial interface. Receive and transmit clock signals can be configured to allow the receive or transmit data to be clocked on either rising or falling edges of the clock signals. Other parameters can also be configured.