MPC8321EVRADDC datasheet(65/82 Pages) FREESCALE

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MPC8323E PowerQUICC II Pro Integrated Communications Processor Family Hardware Specifications, Rev. 4

Freescale Semiconductor

Clocking

22.1

Clocking in PCI Host Mode

When the MPC8323E is configured as a PCI host device (RCWH[PCIHOST] = 1), CLKIN is its primary

input clock. CLKIN feeds the PCI clock divider (

÷2) and the PCI_SYNC_OUT and PCI_CLK_OUT

multiplexors. The CFG_CLKIN_DIV configuration input selects whether CLKIN or CLKIN/2 is driven

out on the PCI_SYNC_OUT signal.

PCI_SYNC_OUT is connected externally to PCI_SYNC_IN to allow the internal clock subsystem to

synchronize to the system PCI clocks. PCI_SYNC_OUT must be connected properly to PCI_SYNC_IN,

with equal delay to all PCI agent devices in the system.

22.1.1

PCI Clock Outputs (PCI_CLK_OUT[0:2])

When the MPC8323E is configured as a PCI host, it provides three separate clock output signals,

PCI_CLK_OUT[0:2], for external PCI agents.

When the device comes out of reset, the PCI clock outputs are disabled and are actively driven to a steady

low state. Each of the individual clock outputs can be enabled (enable toggling of the clock) by setting its

corresponding OCCR[PCICOEn] bit. All output clocks are phase-aligned to each other.

22.2

Clocking in PCI Agent Mode

When the MPC8323E is configured as a PCI agent device, PCI_CLK is the primary input clock. In agent

mode, the CLKIN signal should be tied to GND, and the clock output signals, PCI_CLK_OUTn and

PCI_SYNC_OUT, are not used.

22.3

System Clock Domains

As shown in Figure 43, the primary clock input (frequency) is multiplied up by the system phase-locked

loop (PLL) and the clock unit to create three major clock domains:

•

The coherent system bus clock (csb_clk)

•

The QUICC Engine clock (ce_clk)

•

The internal clock for the DDR controller (ddr_clk)

•

The internal clock for the local bus controller (lb_clk)

The csb_clk frequency is derived from a complex set of factors that can be simplified into the following

equation:

csb_clk = [PCI_SYNC_IN × (1 + ~CFG_CLKIN_DIV)] × SPMF

In PCI host mode, PCI_SYNC_IN × (1 + ~CFG_CLKIN_DIV) is the CLKIN frequency.

The csb_clk serves as the clock input to the e300c2 core. A second PLL inside the core multiplies up the

csb_clk frequency to create the internal clock for the core (core_clk). The system and core PLL multipliers

are selected by the SPMF and COREPLL fields in the reset configuration word low (RCWL) which is

loaded at power-on reset or by one of the hard-coded reset options. See the “Reset Configuration” section

in the MPC8323E PowerQUICC II Pro Communications Processor Reference Manual for more

information.

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