PI7C9X110 datasheet(21/145 Pages) PERICOM

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PI7C9X110

PCIe-to-PCI Reversible Bridge

Page 21 of 145

Pericom Semiconductor

November 2007, Revision 2.4

If PI7C9X110 sees a logic LOW on PCIXCAP, one or more devices on the secondary have either pulled the signal

to ground (PCI-X 66MHz capable) or tied it to ground (only capable of conventional PCI mode). To differentiate

between the two conditions, PI7C9X110 then enables PCIXUP to put the strong pull-up into the circuit node. If

PCIXCAP remains at logic LOW, it must be tied to ground by one or more devices, and the bus is initialized to

conventional PCI mode. If PCIXUP can be pulled up, one or more devices are capable of only PCI-X 66MHz

operation so the bus is initialized to PCI-X 66MHz mode. If PI7C9X110 sees logic HIGH on PCIXCAP, then all

devices on the secondary bus are capable of PCI-X 100MHz or 133MHz operation. Since PI7C9X110 does not have

a pin to distinguish between the 100MHz or 133MHz clock frequencies, its logic is based on 133MHz. The

secondary bus is initialized to PCI-X 133MHz mode. However, 100MHz clock can still be used if all the devices on

the PCI-X bus are 100MHz capable and the clock input (pin CLKIN) is set at 100MHz frequency.

There is no pin for M66EN for the secondary interface of PI7C9X110 because the internal PLL is bypassed in

conventional PCI mode. CLKIN is used directly, eliminating the need to distinguish between conventional PCI

33MHz and 66MHz.

Figure 3-1 PCI / PCI-X Selection

3.3

PIN STRAPPING

If TM2 is strapped to high, PI7C9X110 uses TM1, TM0, and MSK_IN as strapping pins. The strapping functions

are listed in Table 3-2 to show the states of operations during the PCI Express PERST_L de-assertion transition in

forward bridge mode or PCI RESET_L de-assertion transition in reverse bridge mode.

Table 3-2 Pin Strapping

TM2 Strapped

TM1 Strapped

TM0 Strapped

MSK_IN Strapped

Test Functions

PI7C9X110

PCIXCAP

Enable During Bus Capability

Determination

3.3v

PCIXUP

3.3v

56K

Ohms

Weak

Pull-up

PCI-X 100MHz

or 133MHz Card

0.01uF

PCI Card

0.01uF

PCI-X 66MHz

Card

10K

Ohms

0.01uF

Strong

Pull-up

Ohms

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