Service manual

System Overview 1-59
The system box local I/O riser module provides two I/O port interfaces to the
QBB I/O port (IOP). Since there is a similar I/O riser in the PCI box, it is
helpful to name the riser connected to the QBB the local riser and the one
connected to the PCI the remote riser.
Figure 1–25 shows a block diagram of the system box local riser. There are two
minilink application-specific integrated circuits (MLK ASIC) on the module, one
for each port. The function of the minilink is to control the flow of data between
the QBB and the I/O subsystem. The module can be hot swapped if there is
appropriate operating system support.
The MLK ASICs are synchronized to the QBB using a phase locked loop device
that receives its reference clock from the QBB.
The Port In and Port Out signals provide a full duplex link between the MLK
ASIC and the IOP on the QBB. The Port signals include 16 address lines, 16
data lines, and various control lines.
The Cable In and Cable Out signals provide a full duplex link between near end
(Local) and far end (Remote) MLK ASICs through the I/O Hose cable. The cable
signals include 16 multiplexed address/data lines and various control lines.
A 256x8-bit I
2
C EEPROM present on the module sits on I
2
C bus 2 controlled by
the PSM. The contents of this EEPROM can be read using the show fru SCM
command.
LEDs
Power On LED
(Green)
On (normal)
Off
Power is applied to the module
Power not applied to the module
Swap OK LED
(Yellow)
On
Off (normal)
Module safe to hot swap (green LED Off)
Module not safe to hot swap
A short-circuit protection (SCP) daughtercard is provided to monitor the +1.5V,
+3.3V, and +3.3V PLL supply rails; it shuts the power down quickly if a short is
detected on the module.