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176 21555 Non-Transparent PCI-to-PCI Bridge User Manual
List of Registers
Table 108. Primary Expansion ROM Setup Register
This register may be preloaded by serial ROM or programmed by the local processor before host
configuration.
• Primary byte offset: C3:C0h
• Secondary byte offset: C3:C0h
Bit Name R/W Description
11:0 Reserved R Reserved. Read only as 0.
23:12 Size R/(WS)
These bits specify the size of the address range requested by the Primary
Expansion ROM Base Address register.
• When a bit is 1, the corresponding bit in the Primary Expansion ROM
Base Address register functions as a readable and writable bit.
• When a bit is 0, the corresponding bit in the Primary Expansion ROM
Base Address register functions as a read
-only bit that always returns
zero when read.
• Reset value is 0 (disabled).
24 BAR_Enable R/(WS)
The location of this bit in the preload sequence, as listed in “Serial Preload
Sequence” on page 16-180.
• When 0, the
Primary Expansion ROM BAR is disabled and reads
as 0.
• When 1, the
Primary Expansion ROM BAR is enabled, with size
specified by this setup register.
• Reset value is 0
31:25 Reserved R Reserved. Returns 0 when read.