Technical data

Block Diagram
A-12
PCI Bus Expansion
The MLB supports nine PCI slots, including a shared PCI/ISA slot. Full bus
mastering is supported on all nine PCI slots, allowing any PCI master peer-to-peer
access to any PCI slave.
PCI-to-PCI Bridge (PPB)
The 31152 chip on the MLB provides the PCI-to-PCI bridge between the Primary PCI
bus and the Secondary PCI bus. It provides concurrent primary and secondary bus
operations to isolate traffic. It implements delayed transactions for all PCI
configuration, I/O, and memory read commands up to three transactions
simultaneously in each direction. It also allows 72 bytes of read data buffering in
each direction. The PPB also provides VGA addressing and palette support for video
graphics. And it has an ISA-awareness mode for legacy option support.
ISA Bus
The ISA bus supports two ISA bus slots, including one shared PCI/ISA slot. ISA bus
mastering is supported on both ISA slots. The ISA bus operates at 8.33 MHz.
System Management
The 8031 subsystem, shown in Figure A-1, provides system management resources
on an inter-integrated circuit bus (I
2
C bus). The 8031 subsystem detects such items
as fan failure, out-of-voltage range, and excessive temperature, include the
temperature of the two processors. A Watchdog timer monitors the dc power and
turns off the system power if needed. The 8031 has an external SRAM, so the
resources can be accessed, detected, or changed by software. A management
software package, such as ServerWORKS Manager, can be used to manage these
system resources.