Digital Equipment Digital AlphaStation 200 Series Technical Information page 48

Configuring Your AlphaStation System
__________________________NOTE ____________________________
Only a single IDSEL can be asserted in the configuration space address.
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Table 2-7 shows the relationship of the IDSEL bit, PCI base address, and CPU base
address in the AlphaStation 200 Series and the AlphaStation 400 Series systems.
Table 2-7. PCI AD <n> to IDSEL# Assignments
Device
SCSI
ISA Bridge
Ethernet (embedded)
PCI Bus Slot #1
PCI Bus Slot #2
PCI Bus Slot #1
PCI Bus Slot #2
PCI Bus Slot #3
CPU base address <20:16> represents the encoded value of the IDSEL bit to be asserted
(IDSEL bits range from PCI AD<31:11>). For example, in a CPU base address of
1.e006.0000, the encoded IDSEL value is 06. Starting at PCI AD<11> and counting up 7
bits (0-6), points to PCI AD<17>, which is hardwired as an IDSEL line to the SCSI
controller.
When a device is addressed using its IDSEL signal, the low eight bits of the PCI physical
address generated by the CPU select one of 256 possible byte-wide registers within the
device. Of these, 64 are pre-defined as a "header" region whose format is fixed for all PCI
devices; the remaining 192 bytes are device-specific. Figure 2-3 shows the layout of the
64-byte header region.
2-10
IDSEL Bit PCI
Base Address
Both AlphaStation Series Systems
AD[17] 0002.0000
AD[18] 0004.0000
AlphaStation 200 Series System Only
AD[22] 0040.0000
AD[23] 0080.0000
AD[24] 0100.0000
AlphaStation 400 Series System Only
AD[22] 0040.0000
AD[23] 0080.0000
AD[24] 0100.0000
CPU
Base Address
1 E006.0000
1 E007.0000
1 E00B.0000
1 E00C.0000
1 E00D.0000
1 E00B.0000
1 E00C.0000
1 E00D.0000