Service manual

System Overview 1-69
Figure 1–30 shows both a block diagram of the short-circuit protection module
and its interconnect in the QBB and drawer. Similar interconnects exist in the
PCI where the SCP is installed on the PCI backplane, the two remote I/O risers,
and the standard I/O module.
At present (August 2000), the functions performed by the SCP are designed into
the CPU module, the H-switch, the global port, and the GS80 backplane. If the
GS160/320 backplane or other modules are redesigned, the protection circuit
will become part of the modules and the use of the SCP daughtercard will be
eliminated.
The SCP (54-30058-01) is currently used on the memory, directory, local I/O
riser, QBB backplane, and the standard I/O module.
The SCP (54-30394-01) is currently used only on the remote I/O riser.
The first voltage available to the SCP is the +3.3VP for the clocks; the other
voltages are available later in the power-up process and are provided to other
op-amp comparitors as power-up progresses.
The following circuits are monitored:
• 3.3PLL
• 3.3V logic
• 2.5V logic
• 1.5V
• 5V PCI
• 3.3V PCI
Depending upon the location of a short circuit, the SCP latches the main and
auxiliary power modules off in the QBB, or latches the two PCI power supplies
off in the PCI box, or latches the H-switch power supplies off in the H-switch.
Notification of a short-circuit failure is given to the PSM, PBM, or the HPM. In
systems with more than one QBB only the QBB with the short-circuit is
powered off.
To restore power to a QBB after a short-circuit protection fault, either the
system must be power cycled by the OCP switch or the SCM monitor command
power on – csb x (where x is the csb address of the PSM in the target QBB)
must be executed.
If an SCP is not installed, the system will not power up.