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82801AA and 82801AB ICH Datasheet
7-11
Hub Interface-to-PCI Bridge Registers (D30:F0)
7.1.24
BRIDGE_CNT—Bridge Control Register (HUB-PCI—D30:F0)
Offset Address:
Default Value:
3E–3Fh
0000h
Attribute:
Size:
R/W
16 bits
Bit
Description
15:8
Reserved.
7
Fast Back to Back Enable—RO. Hardwired to ‘0’. The PCI logic will not generate fast back-to-back
cycles on the PCI bus.
6
Secondary Bus Reset—RO. hardwired to ‘0’. The ICH does not follow the P2P bridge reset scheme;
Software-controlled resets are implemented in the PCI-LPC device.
5
Master Abort Mode—R/W.
The ICH ignores this bit. However, this bit is read/write for software
compatibility. The ICH must handle master aborts as if this bit is reset to 0.
4
Reserved.
3
VGA Enable—R/W.
1 =Enable. Indicates that the VGA device is on PCI. Therefore, the PCI to hub interface decoder will
not accept memory cycles in the range A0000h
–
BFFFFh. Note that the ICH will never take I/O
cycles in the VGA range from PCI.
0 =Disable
2
ISA Enable—R/W.
The ICH ignores this bit. However, this bit is read/write for software compatibility.
Since the ICH forwards all I/O cycles that are not in the USB, AC’97, or IDE ranges to PCI, this bit
would have no effect.
1
SERR# Enable—R/W.
1 =Enable. If this bit is set AND bit 8 in CMD register (D30:F0 Offset 04h) is also set, the ICH will
set the SSE bit in PD_STS register (D30:F0, offset 06h, bit 14) AND also generate an NMI (or
SMI# if NMI routed to SMI) when the SERR# signal is asserted.
0 =Disable
0
ICH (82801AA):
Parity Error Response Enable—R/W.
1 = Enable the hub interface to PCI bridge for parity error detection and reporting on the PCI bus.
Parity errors on PCI will cause an NMI, if NMI’s are enabled.
0 = Disable
Note: If parity error checking is enabled (either with this bit or D31:F0, PCICMD[bit 6]), then parity
errors on PCI will cause an NMI, if NMI’s are enabled. Some operating systems will not
attempt to recover from this NMI, since it considers the detection of a PCI error as a
castastrophic event.
ICH0 (82801AB):
Parity Error Response Enable—RO. Hardwired to ‘0’.