5.3IDSEL Lines
The IDSEL lines act as chip selects during the configuration cycles. Configuration cycles allow read and write access to one of the device configuration space registers. As in PCI, the IDSEL lines can be mapped to upper address lines, which are unused during the configuration cycles.
5.3.1Primary IDSEL Line
Figure 5 provides an example of the 31154 used as an embedded controller connected to four PCI devices. Note that AD16 is typically reserved for a PCI/PCI-X bridge.
•When the 31154 is used as the primary interface to a plug-in card, the primary IDSEL line must be routed from the PCI connector to the P_IDSEL pin.
•When the 31154 is used in an embedded application, PCI AD16 is used for source bridges. This line (AD16) must be connected to the P_IDSEL line through a 2 KΩ resistor.
Figure 5. | IDSEL Mapping |
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5.3.2Secondary IDSEL Lines
The PCI specification recommends a specific resistor value of 2 KΩ ±5%. A smaller value may be used as long as system analysis ensures that timing and noise budgets for the AD bit are met.
30 | Intel® 31154 133 MHz PCI Bridge Design Guide Design Guide |