MPC8535E datasheet(92/126 Pages) FREESCALE

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MPC8535E PowerQUICC III Integrated Processor Hardware Specifications, Rev. 3

High-Speed Serial Interfaces

Freescale Semiconductor

— The external reference clock driver must be able to drive this termination.

— The SerDes reference clock input can be either differential or single-ended. See the Differential Mode and

Single-ended Mode description below for further detailed requirements.

•

The maximum average current requirement that also determines the common mode voltage range

— When the SerDes reference clock differential inputs are DC coupled externally with the clock driver chip, the

maximum average current allowed for each input pin is 8mA. In this case, the exact common mode input voltage

is not critical as long as it is within the range allowed by the maximum average current of 8 mA (refer to the

following bullet for more detail), since the input is AC-coupled on-chip.

— This current limitation sets the maximum common mode input voltage to be less than 0.4 V (0.4 V/50 = 8 mA)

while the minimum common mode input level is 0.1V above SnGND (xcorevss). For example, a clock with a

50/50 duty cycle can be produced by a clock driver with output driven by its current source from 0mA to 16mA

(0–0.8 V), such that each phase of the differential input has a single-ended swing from 0 V to 800mV with the

common mode voltage at 400mV.

— If the device driving the SDn_REF_CLK and SDn_REF_CLK inputs cannot drive 50

Ω to SnGND (xcorevss)

DC, or it exceeds the maximum input current limitations, then it must be AC-coupled off-chip.

•

The input amplitude requirement

— This requirement is described in detail in the following sections.

Figure 58. Receiver of SerDes Reference Clocks

Input

Amp

SDn_REF_CLK

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