SB82371 Intel Corporation, SB82371 Datasheet - Page 23

• Manufacturer Part Number: SB82371
• Description: 82371FB (PIIX) AND 82371SB (PIIX3) PCI ISA IDE XCELERATOR
• Manufacturer: Intel Corporation

ISA Compatible Registers
The ISA-Compatible registers (e.g., DMA registers, timer/counter registers, X-Bus registers, and NMI
registers) are accessed through normal I/O space. Except for the DMA registers, the PIIX/PIIX3 positively
decodes accesses to the ISA-Compatible registers. The PIIX/PIIX3 subtractively decodes accesses to all I/O
space registers contained within the ISA-Compatible DMA function. This permits another device in the
system to implement the compatible DMA function.
PCI master accesses to the ISA-Compatible registers can be 8, 16, 24, or 32 bits. However, the PIIX/PIIX3
only responds to the least significant byte. On writes the other bytes are not loaded and on reads the other
bytes have invalid data. The PIIX/PIIX3 responds as an 8-bit ISA I/O slave when accessed by an ISA master.
See the PCI Local Bus IDE section for accesses to the IDE register blocks located in the IDE device
In general, accesses from CPU or PCI masters to the internal PIIX/PIIX3 registers are not broadcast to the
ISA Bus. Exceptions to this are read/write accesses to 70h and F0h and write accesses to 80h, 84–86h, 88h,
8C–8Eh, 90h, 94–96h, 98h, and 9C–9Eh. These accesses are broadcast to the ISA Bus. Note that aliasing of
the 90–9Fh to 80–8Fh can be enabled/disabled via the ISA Controller Recovery Timer Register.
Power Management Registers
There are two power management registers located in normal I/O space. These registers are accessed (by
PCI Bus masters) with 8-bit accesses. The other power management registers are located in PCI
configuration space for function 0.
PCI Bus Master IDE Registers
The PCI Bus master IDE function uses 16 bytes located in normal I/O space, allocated via the BMIBA
register (a PCI base address register). All bus master IDE I/O space registers can be accessed as 8, 16, or
32-bit quantities.
Universal Serial Bus Registers
A set of USB registers provide control and status information for the Host Controller and two USB ports
(Table 7). This block of registers is I/O mapped into PCI I/O space and control variouos operations of the
USB Host Controller. The registers are relocateable via the USBBASE Register which is located in function 0
PCI configuration space.
00–01h
02–03h
04–05h
06–07h
08h
09 0Bh
0C–0Dh
0Eh
Configuration
Offset
Table 2. PCI Configuration Registers—Function 0 (PCI to ISA Bridge)
VID
DID
PCICMD
PCISTS
RID
CLASSC
—
HEDT
Mnemonic
Vendor Identification
Device Identification
PCI Command
PCI Device Status
Revision Identification
Class Code
Reserved
Header Type
Register
82371FB (PIIX) AND 82371SB (PIIX3)
RO
RO
R/W
R/WC
RO
RO
—
RO
Register
Access
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