Installation guide

Software Configuration 5-25

Additional Configuration Tasks

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.

If the network processor module is operating as DTE in NRZI mode, the sense of the

dte-invert-timing command must be manually changed. For instance, if the command

no dte-invert-timing was previously entered in the conﬁguration ﬁle, then

dte-invert-timing must be conﬁgured for the module to operate as DTE in NRZI mode.

Conﬁguring NRZI Format on Serial Interfaces

All interfaces support both nonreturn to zero (NRZ) and NRZI formats. Both formats 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. Refer to the Cisco IOS conﬁguration guides and command references for

complete command descriptions and instructions.