Configuring the Serial Clocking Mode

By default, serial interfaces use loop clocking mode. For EIA-530 and V.35 interfaces, you can configure each port on the PIC independently to use loop, DCE, or DTE clocking mode. For X.21 interfaces, only loop clocking mode is supported.

The three clocking modes work as follows:

• Loop clocking mode—Uses the DCE’s RX clock to clock data from the DCE to the DTE.
• DCE clocking mode—Uses the TXC clock, which is generated by the DCE specifically to be used by the DTE as the DTE’s transmit clock.
• DTE clocking mode—Also known as line timing, uses an internally generated clock. You can configure the speed of this clock by including the clock-rate statement at the [edit interfaces se-pim/0/port serial-options] or [edit interfaces se-fpc/pic/port dte-options] hierarchy levels. For more information about the DTE clock rate, see Configuring the DTE Clock Rate.

Note that DCE clocking mode and loop clocking mode use external clocks generated by the DCE.

Figure 15 shows the clock sources of loop, DCE, and DTE clocking modes.

Figure 15: Serial Interface Clocking Mode

To configure the clocking mode of a serial interface, include the clocking-mode statement:

You can include the clocking-mode statement at the following hierarchy levels:

• [edit interfaces se-pim/0/port serial-options]
• [edit interfaces se-fpc/pic/port serial-options]

• Inverting the Serial Interface Transmit Clock
• Configuring the DTE Clock Rate

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