3-22
Cisco ONS 15530 Configuration Guide and Command Reference
78-14227-01, Cisco IOS Release 12.1(10)EV2
Chapter3 Initial Configuration
About the Software Configuration Register
•Enable booting from a TFTP server
•Recover a lost password
•Boot the system manually using the boot command at the bootstrap program prompt.
•Force the system to boot automatically from the system bootstrap software (boot image) or from its
default system image in onboard Flash memory, using any boot system commands stored in the
startup configuration file in NVRAM
Software Configuration Register Settings
Table 3 -4 describes each of the software con figurati on regist er bi ts.
Caution To avoid confusion and possibly halting the system, remember that valid configuration register
settings might be combinations of settings and not just the individual settings listed in Table 3- 4.
For example, the value of 0x0101 is a combination of settings (bit 8 is 0x0100 and bits 00 through 0 3
are 0x0001).
Bit 8 controls the console break function. Setting bit8 (the factory default) causes the system to ignore
the console break key. Clearing bit 8 causes the system to use the break key or break sig nal as a command
to force the system into the bootstrap monitor (ROMMON), thereby halting normal operation.
Regardless of the setting of the break enable bit, a break causes a return to the ROMMON during the
first few seconds (approximately five seconds) of booting.
Bit 9 controls the secondary bootstrap program function. Settin g b it 9 cause s the syst em to u se t he
secondary bootstrap. Clearing bit 9 (the factory default) causes the system to ignore the secondary
bootstrap. The secondary bootstrap program is used for system debugging and diagnostics.
Bit 10 contro ls the host por tion of the IP br oadcas t address. Se tting bit 10 causes the system to use all
zeros. Clearing bit10 ( the factory default) causes the system to use all ones. Bit10 interacts with bit 14,
which controls the network and subnet portions of the IP broadcast address.
Table 3 -5 shows the combined effect of bits 14 and 10.
Table3-4 Software Configuration Register Bits
Bit Number Hexadecimal Description
00 to 03 0x0000 to 0x000F Controls the system boot behavior (also known as the boot field)
06 0x0040 Causes system software to ignore NVRAM contents
07 0x0080 Enables the OEM bit
08 0x0100 Disables the break function
09 0x0200 Uses secondary bootstrap d uring sy stem boot
10 0x0400 Uses an IP broadcast with all zeros
11 to 12 0x0800 to 0x1000 Sets the console line speed (default is 9600 baud)
13 0x2000 Boots the default Flash software if network boot fails
14 0x4000 Uses IP broadcasts without network nu mb ers
15 0x8000 Enables diagnostic messages and ignores the NVRAM contents