Specifications

Configure DTR Signal Pulsing

Configuring Serial Interfaces IC-77

Conﬁgure DTR Signal Pulsing

You can conﬁgure pulsing DTR signals on all serial interfaces. When the serial line protocol goes

down (for example, because of loss of synchronization) the interface hardware is reset and the DTR

signal is held inactive for at least the speciﬁed interval. This function is useful for handling

encrypting or other similar devices that use the toggling of the DTR signal to resynchronize. To

conﬁgure DTR signal pulsing, use the following command in interface conﬁguration mode:

Ignore DCD and Monitor DSR as Line Up/Down Indicator

This task applies to Quad Serial NIM interfaces on the Cisco 4000 series and Hitachi-based serial

interfaces on the Cisco 2500 series and Cisco 3000 series.

By default, when the serial interface is operating in DTE mode, it monitors the Data Carrier Detect

(DCD) signal as the line up/down indicator. By default, the attached DCE device sends the DCD

signal. When the DTE interface detects the DCD signal, it changes the state of the interface to up.

In some conﬁgurations, such as an SDLC multidrop environment, the DCE device sends the Data

Set Ready (DSR) signal instead of the DCD signal, which prevents the interface from coming up. To

tell the interface to monitor the DSR signal instead of the DCD signal as the line up/down indicator,

use the following command in interface conﬁguration mode:

Unless you know for certain that you really need this feature, be very careful using this command.

It will hide the real status of the interface. The interface could actually be down and you will not

know by looking at show displays.

Specify the Serial Network Interface Module Timing

On Cisco 4000 series routers, you can specify the serial Network Interface Module timing signal

conﬁguration. When the board is operating as a DCE and the DTE provides terminal timing (SCTE

or TT), you can conﬁgure the DCE to use SCTE from the DTE. When running the line at high speeds

and long distances, this strategy prevents phase shifting of the data with respect to the clock.

To conﬁgure the DCE to use SCTE from the DTE, use the following command in interface

conﬁguration mode:

When the board is operating as a DTE, you can invert the TXC clock signal it gets from the DCE

that the DTE uses to transmit data. Invert the clock signal if the DCE cannot receive SCTE from the

DTE, the data is running at high speeds, and the transmission line is long. Again, this prevents phase

shifting of the data with respect to the clock.

Command Purpose

pulse-time seconds Conﬁgure DTR signal pulsing.

Command Purpose

ignore-dcd Conﬁgure the serial interface to monitor the DSR

signal as the line up/down indicator.

Command Purpose

dce-terminal-timing enable Conﬁgure the DCE to use SCTE from the DTE.