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PI7C8154B
ASYNCHRONOUS 2-PORT
PCI-to-PCI BRIDGE
Advance Information
Page 33 of 112
JUNE 2008 REVISION 1.1
The lowest two address bits on P_AD[1:0] are 01b.
The bus number in address field P_AD[23:16] is equal to the value in the secondary bus
number register in configuration space.
The bus command on P_CBE[3:0] is a configuration read or configuration write transaction.
When PI7C8154B translates the Type 1 transaction to a Type 0 transaction on the secondary
interface, it performs the following translations to the address:
Sets the lowest two address bits on S_AD[1:0] to 0.
Decodes the device number and drives the bit pattern specified in Table 2-6 on S_AD[31:16]
for the purpose of asserting the device’s IDSEL signal.
Sets S_AD[15:11] to 0.
Leaves unchanged the function number and register number fields.
PI7C8154B asserts a unique address line based on the device number. These address lines may be
used as secondary bus IDSEL signals. The mapping of the address lines depends on the device
number in the Type 1 address bits P_AD[15:11]. Table 2-6 presents the mapping that PI7C8154B
uses.
Table 2-6 DEVICE NUMBER TO IDSEL S_AD PIN MAPPING
Device Number
P_AD[15:11]
Secondary IDSEL S_AD[31:16]
S_AD
0h
00000
0000 0000 0000 0001
16
1h
00001
0000 0000 0000 0010
17
2h
00010
0000 0000 0000 0100
18
3h
00011
0000 0000 0000 1000
19
4h
00100
0000 0000 0001 0000
20
5h
00101
0000 0000 0010 0000
21
6h
00110
0000 0000 0100 0000
22
7h
00111
0000 0000 1000 0000
23
8h
01000
0000 0001 0000 0000
24
9h
01001
0000 0010 0000 0000
25
Ah
01010
0000 0100 0000 0000
26
Bh
01011
0000 1000 0000 0000
27
Ch
01100
0001 0000 0000 0000
28
Dh
01101
0010 0000 0000 0000
29
Eh
01110
0100 0000 0000 0000
30
Fh
01111
1000 0000 0000 0000
31
10h – 1Eh
10000 – 11110
0000 0000 0000 0000
-
1Fh
11111
Generate special cycle (P_AD[7:2] = 00h)
0000 0000 0000 0000 (P_AD[7:2] = 00h)
-
PI7C8154B can assert up to 16 unique address lines to be used as IDSEL signals for up to 16
devices on the secondary bus, for device numbers ranging from 0 through 8. Because of electrical
loading constraints of the PCI bus, more than 16 IDSEL signals should not be necessary. However,
if device numbers greater than 16 are desired, some external method of generating IDSEL lines
must be used, and no upper address bits are then asserted. The configuration transaction is still
translated and passed from the primary bus to the secondary bus. If no IDSEL pin is asserted to a
secondary device, the transaction ends in a master abort.
PI7C8154B forwards Type 1 to Type 0 configuration read or write transactions as delayed
transactions. Type 1 to Type 0 configuration read or write transactions are limited to a single 32-bit
data transfer.