User guide

9
Nbus
The Nbus is a special case of an ISA bus. The Nbus is a simple 8-bit data,
16-bit address, nonmultiplexed resource bus that interfaces with the PCI bus
through the Super I/O (SIO) chip (Intel 82378IB). The interface translates PCI
I/O references to the Nbus into simple read and write cycles to the resources
hanging off the Nbus lines, as shown in Figure 9–1.
Figure 9–1 Nbus and Nbus Resources
Nbus
Interface
(SIO)
Interrupt
Controller
Flash
Super
I/O
Keyboard
and Mouse
Controller
Interval
Timer
TOY Clock
Watchdog Timer
NVRAM
(DS1386)
Nbus 8 Bits
ML013286
9.1 Nbus Address Space
The bottom 64K of PCI sparse I/O address space is mapped onto the Nbus for use
by the:
• Keyboard and mouse controller
• Super I/O
• Module registers
Nbus 9–1