MPC8248VR datasheet(27/61 Pages) FREESCALE

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MPC8272 PowerQUICC II Family Hardware Specifications, Rev. 3

Freescale Semiconductor

Clock Configuration Modes

As shown in this table, the clocking mode is set according to two sources:

•

PCI_CFG[0]— An input signal. Also defined as “PCI_HOST_EN.” See Chapter 6, “External

Signals,” and Chapter 9, “PCI Bridge,” in the SoC reference manual.

•

PCI_MODCK—Bit 27 in the Hard Reset Configuration Word. See Chapter 5, “Reset,” in the SoC

reference manual.

Within each mode, the configuration of bus, core, PCI, and CPM frequencies is determined by seven bits

during the power-on reset—three hardware configuration pins (MODCK[1–3]) and four bits from

hardware configuration word[28–31] (MODCK_H). Both the PLLs and the dividers are set according to

the selected clock operation mode as described in the following sections.

NOTE

Clock configurations change only after PORESET is asserted.

NOTE: Tval (Output Hold)

The minimum Tval = 2 ns when PCI_MODCK = 1, and the minimum

Tval = 1 ns when PCI_MODCK = 0. Therefore, designers should use clock

configurations that fit this condition to achieve PCI-compliant AC timing.

7.1

PCI Host Mode

These tables show configurations for PCI host mode. The frequency values listed are for the purpose of

illustration only. Users must select a mode and input bus frequency so that the resulting configuration does

not exceed the frequency rating of the user’s device. Note that in PCI host mode the input clock is the bus

clock.

Table 16. SoC Clocking Modes

Pins

Clocking Mode

PCI Clock Frequency Range (MHz)

Reference

PCI_CFG[0]1

1 PCI_HOST_EN

PCI_MODCK2

2 Determines PCI clock frequency range.

PCI host

50–66

Table 17

25–50

Table 18

PCI agent

50–66

Table 19

25–50

Table 20

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