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Updated:December 1, 2022
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This document describes the standard break key sequence combinations for the operating systems and how to fix any issues.
There are no specific requirements for this document.
This document is not restricted to specific software and hardware versions.
The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, ensure that you understand the potential impact of any command.
The Electronic Industries Association RS-232 logic level uses +3 to +25 volts to signify a Space (Logic 0) and -3 to -25 volts for a Mark (logic 1). A break signal is when the data line remains in the space condition for a specified duration, usually 100 ms to ½ second. All characters begin with a start bit and end with a stop bit (and also a parity bit or two). The level condition of the start and stop bits is always opposite. So, no character combination can look like the break signal. A break signal enables you to access a ROM Monitor on Cisco IOS® devices when a password recovery is necessary.
Standard Break Key Combinations
Hyperterminal (version 595160)
DOS or Windows
Ctrl-], then type send brk
Telnet to Cisco
Ctrl-], then Break or Ctrl-c
VT 100 Emulation
Shift-6 Shift-4 Shift-b (^$B)
Connect pin 2 (X-mit) to +V for half a second
Cisco to aux port
Control-Shft-6, then b
How to Troubleshoot Issues
Problems that you encounter during password recovery often occur because you are not sure about what the break key sequence is for the (non-Cisco) software you use. For software not listed in the table, and for additional information, refer to the documentation of the individual software packages.
The auxiliary (AUX) port is not active during the boot sequence of a router. Therefore, it is no use if you send a break through the AUX port. You need to have connection to the console port, and have these settings:
9600 baud rate
8 data bits
1 stop bit
No flow control
Some versions of Windows NT have hyperterminal software that cannot send the correct break key signal. Refer toHilgraeve Hyperterminal Emulation Program for more information and for an upgrade of the hyperterminal software.
In some cases, the break sequence can be transmitted improperly when a USB/Serial converter cable is used. In such cases, use a keyboard with a different connector port (for example, a PS/2).
How to Simulate a Break Key Sequence
Break key sequence simulation is useful if your terminal emulator does not support the break key, or if a bug does not allow your terminal emulator to send the correct signal.
Note: The hyperterminal under Windows NT had this behavior in the past.
Complete these steps to simulate a break key sequence:
Connect to the router with these terminal settings:
1200 baud rate
8 data bits
1 stop bit
No flow control
You no longer see any output on your screen, and this is normal.
Power cycle (switch off and then on) the router and press the SPACEBAR for 10-15 seconds in order to generate a signal similar to the break sequence.
Disconnect your terminal, and reconnect with a 9600 baud rate. You enter the ROM Monitor mode.
If all these methods fail to properly send a break, retry the procedures from a different terminal or PC platform.