Datasheet

Installing 2T16S Network Processor Modules in the Cisco 4000 Series

78-3277-03

When a port is operating in DCE mode, the default operation is for the attached DTE device to return

the clock signal (SCTE) to the DCE port. The DCE sends SCT and SCR clock signals to the DTE, and

the DTE returns an SCTE clock signal to the DCE. If the DTE device does not return SCTE, you must

use the dce-terminal-timing-enable command to configure the DCE port to use its own clock signal in

place of the SCTE signal that would normally be returned from the DTE device.

To configure an interface to accept the internal clock generated by the serial module in place of the SCTE

clock that is normally returned by the DTE device, specify the interface followed by the

dce-terminal-timing-enable command. In the example that follows, the serial 0 port has been

configured to accept the internal clock signal:

interface serial 0

dce-terminal-timing-enable

To turn off this command, use the no dce-terminal-timing-enable command.

When the serial port is a DTE, the invert-txc command inverts the TXC clock signal it receives from the

remote DCE. When the serial port is a DCE, this command inverts the clock signal to the remote DTE

port. Use the no invert-txc command to change the clock signal back to its original phase. The no

invert-txc command is redundant with the four-port serial module because the module will

automatically discover the polarity of the clock and invert the signal.

Configuring NRZI Format on Serial Interfaces

All interfaces support both NRZ and NRZI formats; which use two different voltage levels for

transmission. NRZ signals maintain constant voltage levels with no signal transitions (no return to a zero

voltage level) during a bit interval and are decoded using absolute values (0 and 1). NRZI uses the same

constant signal levels but interprets the presence of data at the beginning of a bit interval as a signal

transition and the absence of data as no transition. NRZI uses differential encoding to decode signals,

rather than determining absolute values.

NRZ format, the factory default on all interfaces, is the most common. NRZI format is commonly used

with EIA/TIA-232 connections in IBM environments. To enable NRZI encoding on any interface,

specify the port address of the interface followed by the command nrzi-encoding. In the example that

follows, serial port 0 is configured for NRZI encoding:

router# configure terminal

interface serial 0

nrzi-encoding

To disable NRZI encoding on a port, specify the port and use the no nrzi-encoding command. For

complete command descriptions and instructions, refer to the Configuration Fundamentals Command

Reference.

Configuring the Asynchronous/Synchronous Serial Interfaces

The ports you plan to use for asynchronous operation must be reconfigure after the initial setup. The

following steps provide an example of how to configure a synchronous serial port to be an asynchronous

serial port.

Step 1 Enter the command config terminal to enter configuration mode:

Router# config terminal

Router(config)#

The router enters global configuration mode, indicated by the Router(config)# prompt.