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Chapter 4 System Support
Compaq Deskpro 4000N and 4000S Personal Computers
First Edition - September 1997
4-6
Figure 4-3 shows how the loading of 0CF8h results in a Type 0 configuration cycle on the PCI
bus. The Device Number (bits <15..11> determines which one of the AD31..11 lines is to be
asserted high for the IDSEL signal, which acts as a “chip select” function for the PCI device to be
configured.
Figure 4–3. Type 0 Configuration Cycle
Type 0 configuration cycles are used for configuring devices on PCI bus # 0. Type 1
configuration cycles (reg. 0CF8h bits <1,0> = 01b) are passed on to PCI bus # 1 (if present).
Table 4-3 shows the standard configuration of device numbers and IDSEL connections for
components and slots residing on a PCI bus.
Table 4–3. PCI Device Configuration Access
Table 4-3.
PCI Device Configuration Access
PCI Device
Device No.
(CF8h <15..11>)
IDSEL
Wired to:
North Bridge (82C595) 0 AD11
PCI Connector 2 AD13
South Bridge (82C586) 7 AD31
Graphics Controller 15 AD26
Network Interface Controller 16 AD27
The function number (CF8h, bits <10..8>) is used to select a particular function within a
multifunction device as shown in Table 4-4.
AD31..0
w/Type 0
Config. Cycle
Reserved
Device
Number
Function
Number
Register
Index
Bus
Number
3130 24 23
16 15 11 10 8 721 0
0 0
IDSEL (only one signal line asserted)
Function
Number
Register
Index
31
11 10 8
721 0
Register 0CF8h
Results in: