Specifications

OL-4923-01 B0

Software Configuration Register Settings

Settings for the 16-bit software configuration register are written into the NVRAM. Following are some

reasons for changing the software configuration register settings:

• To select a boot source and default boot filename

• To enable or disable the Break function

Note The Break function (software configuration register bit 8) when enabled allows you to send a Break

signal to the router during a system (re)boot. This stops the boot process and places the router into

ROM monitor mode. You can activate the Break function by using a dedicated Break key function on

the keyboard, or by entering the Ctrl-[ (left square bracket) key combination.

• To control broadcast addresses

• To set the console terminal baud rate

• To load operating software from the Flash memory card

• To enable booting from a Trivial File Transfer Protocol (TFTP) server

• To recover a lost password

• To allow you to manually boot the system using the b command at the bootstrap program prompt

• To force the router to boot automatically from the system bootstrap software (boot image) or from

its default system image in onboard Flash memory, and to read any boot system commands that are

stored in the configuration file in NVRAM

If the router finds no boot system commands, it uses the configuration register value to form a filename

from which to boot a default system image stored on a network server. (See Table 20.)

Table 18 lists the meaning of each of the software configuration memory bits, and Table 19 defines the

boot field.

Caution To avoid confusion and possibly halting the router, remember that valid configuration register

settings might be combinations of settings and not just the individual settings listed in Table 18.For

example, the factory default value of 0x0102 is a combination of settings.

Table 18 Software Conﬁguration Register Bit Meanings

Bit Number

Hexadecimal Meaning

00 to 0F 0x0000 to 0x000F Boot field (see Table 19)

06 0x0040 Causes system software to ignore NVRAM contents

07 0x0080 OEM

bit enabled

08 0x0100 Break disabled

09 0x0200 Use secondary bootstrap

10 0x0400 IP broadcast with all zeros

11 to 12 0x0800 to 0x1000 Console line speed (default is 9600 baud)

13 0x2000 Boot default Flash memory software if network boot fails