C-13
Cisco 3900 Series, Cisco 2900 Series, and Cisco 1900 Series Integrated Services Routers Generation 2 Software Configuration Guide
Appendix C Using ROM Monitor
How to Use the ROM Monitor—Typical Tasks
Modifying the Configuration Register (confreg)
This section describes how to modify the configuration register by using the confreg ROM monitor
command. You can also modify the configuration register setting from the Cisco IOS command-line
interface (CLI) by using the config-register command in global configuration mode.
Caution Do not set the configuration register by using the config-register 0x0 command after setting the baud
rate. To set the configuration register without affecting the baud rate, use the current configuration
register setting by entering the show ver | inc configuration command and then replacing the last
(rightmost) number with a 0 in the configuration register command.
Restrictions
The modified configuration register value is automatically written into NVRAM, but the new value does
not take effect until you reset or power-cycle the router.
SUMMARY STEPS
1. confreg [value]
DETAILED STEPS
Examples
In the following example, the configuration register is set to boot the system image from flash memory:
rommon 3 > confreg 0x2102
In the following example, no value is entered; therefore, the system prompts for each bit in the register:
rommon 7 > confreg
Configuration Summary
enabled are:
console baud: 9600
boot: the ROM Monitor
do you wish to change the configuration? y/n [n]: y
enable "diagnostic mode"? y/n [n]: y
enable "use net in IP bcast address"? y/n [n]: y
enable "load rom after netboot fails"? y/n [n]: y
enable "use all zero broadcast"? y/n [n]: y
enable "break/abort has effect"? y/n [n]: y
Command or Action Purpose
Step 1
confreg [value]
Example:
rommon > confreg 0x2102
Changes the configuration register settings while in ROM
monitor mode.
• Optionally, enter the new hexadecimal value for the
configuration register. The value range is from 0x0 to
0xFFFF.
• If you do not enter the value, the router prompts for
each bit of the 16-bit configuration register.
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