Chapter 4 System Support
Compaq Deskpro EX Series of Personal Computers
First Edition - August 2000
4-4
Two types of configuration cycles are used. A Type 0 (zero) cycle is targeted to a device on the
PCI bus on which the cycle is running. A Type 1 cycle is targeted to a device on a downstream PCI
bus as identified by bus number bits <23..16>. With three or more PCI buses, a PCI bridge may
convert a Type 1 to a Type 0 if it’s destined for a device being serviced by that bridge or it may
forward the Type 1 cycle unmodified if it is destined for a device being serviced by a downstream
bridge. Figure 4-2 shows the configuration cycle format and 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. The function number (CF8h, bits <10..8>) is used to
select a particular function within a PCI component.
Figure 4-2.
Configuration Cycle
Table 4-1 shows the standard configuration of device numbers and IDSEL connections for
components and slots residing on a PCI bus.
Table 4-1.
PCI Device Configuration Access
Table 4-1.
PCI Component Configuration Access
PCI Component
Function #
Device #
PCI
Bus #
IDSEL
Wired
to:
82815 GMCH:
Memory Controller
AGP Bridge
i740 Graphics Controller
0
0
0
0 (00h)
1(01h)
2 (02h)
0
0
0
--
AGP slot
0
0 (00h)
1
--
82801AA ICH:
PCI Bridge
LPC Bridge
EIDE Controller
USB I/F
SMBus Controller
Reserved
AC97 Audio Controller
AC97 Modem Controller
0
0
1
2
3
4
5
6
30 (1Eh)
31 (1Fh)
31 (1Fh)
31 (1Fh)
31 (1Fh)
31 (1Fh)
31 (1Fh)
31 (1Fh)
0
0
0
0
0
0
0
0
--
PCI Connector 1 (slot 1)
0
8 (08h)
2 [1]
AD24
PCI Connector 2 (slot 2)
0
9 (09h)
2 [1]
AD25
PCI Connector 3 (slot 3)
0
10 (0Ah)
2 [1]
AD26
NOTES:
[1] Bus number in standard configuration. Can shift up if an AGP device with an additional
PCI bridge is installed in the AGP slot.
Not used.
AD31..0
(w/Type 00
Config. Cycle)
Reserved
Device
Number
Function
Number
Register
Index
Bus
Number
31
24 23
16 15
11 10
8 7
2 1 0 [1]
IDSEL (only one signal line asserted)
Function
Number
Register
Index
Register 0CF8h
Results in:
NOTES:
[1] Bits <1,0> : 00 = Type 0 Cycle, 01 = Type 1 cycle
Type 01 cycle only. Reserved on Type 00 cycle.
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