Datasheet

Register Description
R
Datasheet 139
3.10.9 PBUSN1 - Primary Bus Number (Device #1)
Address Offset: 18h
Default Value: 00h
Access: Read Only
Size: 8 bits
This register identifies that “virtual” PCI to PCI bridge is connected to bus #0.
Bit Description
7:0 Primary Bus Number (BUSN): Configuration software typically programs this field with
the number of the bus on the primary side of the bridge. Since Device #1 is an internal
device and its primary bus is always 0.
3.10.10 SBUSN1 - Secondary Bus Number (Device #1)
Address Offset: 19h
Default Value: 00h
Access: Read/Write
Size: 8 bits
This register identifies the bus number assigned to the second bus side of the “virtual” PCI to PCI
bridge i.e. to PCI_B/AGP. This number is programmed by the PCI configuration software to
allow mapping of configuration cycles to PCI_B/AGP.
Bit Description
7:0 Secondary Bus Number (BUSN): This field is programmed by configuration software
with the bus number assigned to PCI_B.