Troubleshooting Overview
Cisco 12008 Gigabit Switch Router Installation and Configuration Guide
5-6
•Processor subsystem—The processor subsystem includes the RP and all installed line
cards. Each line card has an onboard processor, to which the RP downloads a copy of
the Cisco IOS operating image.
A line card or RP that is not firmly seated in the backplane might cause the system to
hang and crash. Two 4-character alphanumeric displays at the bottom of the RP and each
line card provide status and error messages that can be an aid in troubleshooting.
Identifying Startup Problems
Startup problems are commonly due to problems with source power or to a card that is not
properly seated in the backplane.

Normal System Startup Sequence

Each card installed in the system incorporates an MBus module and at least one DC-DC
converter. The MBus module on each card provides an interface to th e RP via the system’s
maintenance bus (MBus); the MBus module on each card also controls its own onboard
DC-DC converter.
When you first start up the router, the following sequence of events occurs:
•Each MBus module receives +5 VDC directly from the power supply(ies) through the
backplane. When the power supply power switches are turned on, each MBus module
powers up. As it does so, the MBus module processor boots from it s onboard EEPR OM.
•As part of the boot process, each MBus module processor reads a set of ID pins on the
card. These pins, whose meaning is determined at the time of card manufacture, identify
the kind of card on which the MBus module is mounted.
•In the case of the MBus modules on the CSC and the RP, the CSC MBus module
processor immediately enables the card’s DC-DC converter, followed by that of the RP.
(The CSC takes precedence in the system power-up sequence, because it supplies
master clocking services to the entire system.)
If the onboard MBus module determines that it is mounted on a line card or an SFC, the
MBus module remains idle for the time being, leaving the card powered down until it
receives power up instructions from the master MBus module on the RP.