Intel
®
81341 and 81342—Address Translation Unit (PCI-X)
Intel
®
81341 and 81342 I/O Processors
Developer’s Manual
December 2007
136
Order Number: 315037-002US
2.11.6
External Clock Driver (CR_FREQ[1:0])
When the internal PCI Clock outputs are not sufficient, an external clock driver can be
used to supply additional PCI Clocks. To facilitate the use of an external driver, the
CR_FREQ[1:0]
pins are driven based on the settings in the PCI-X capability field (bits
19:16) in the
“PCI Configuration and Status Register - PCSR”
. These output pins can be
connected to a PCI-X clock driver to select the desired bus frequency.
Table 18. CR_FREQ[1:0] Encoding
PCSR[19:16]
(PCIX Init
Pattern)
PCSR[10]
(P_M66EN)
CR_FREQ[1:0]
Bus Frequency
Bus Mode
1111
0
11
33 MHz
Conventional PCI
1111
1
10
66 MHz
Conventional PCI
1110
-
10
66 MHz
PCI-X
1101
-
01
100 MHz
PCI-X
1100
-
00
133 MHz
PCI-X