Installation guide

Software Configuration 5-23

Additional Configuration Tasks

Conﬁguring Timing (Clock) Signals for Serial Interfaces

All interfaces support both data terminal equipment (DTE) and DCE modes, depending on

the mode of the interface cable attached to the port. To use a port as a DTE interface,

connect a DTE adapter cable to the port. When the system detects the DTE mode cable, it

automatically uses the external timing signal. To use a port in DCE mode, you must connect

a DCE interface cable and set the clock speed with the clockrate command. This section

describes how to set the clock rate on a DCE port and, if necessary, how to invert the clock

to correct a phase shift between the data and clock signals.

Note Serial ports conﬁgured as DCE must also be conﬁgured with the clockrate

command. An error message will be generated if there is a mismatch between the cable and

the software conﬁguration of the port—for example, if the cable is DTE and the clock rate

is set, or if the cable is DCE and the clock rate is not conﬁgured.

Setting the Clock Rate on Serial Interfaces

All DCE interfaces require a noninverted internal transmit clock signal, which is generated

by the serial module. The default operation on a DCE interface is for the DCE device to

generate its own transmit clock signal (TXC) and send it to the remote DTE. The remote

DTE device returns the clock signal to the DCE. The clockrate command speciﬁes the rate

as a bits-per-second value. In the following example, the clock rate for the top serial

interface on a dual-port serial module is deﬁned as 72 kbps:

interface serial 1

clockrate 72000