MPC8377ECVRAFDA datasheet(79/124 Pages) FREESCALE

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MPC8377E PowerQUICC™ II Pro Processor Hardware Specifications, Rev. 2

Freescale Semiconductor

High-Speed Serial Interfaces (HSSI)

— The SerDes reference clock input can be either differential or single-ended. Refer to 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 8 mA. 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 0.1 V above

SGND_SRDSn (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 0 mA to 16 mA (0–0.8 V), such

that each phase of the differential input has a single-ended swing from 0 V to 800 mV with the

common mode voltage at 400 mV.

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

Ω to

SGND_SRDSn (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 52. Receiver of SerDes Reference Clocks

21.2.2

DC Level Requirement for SerDes Reference Clocks

The DC level requirement for the device SerDes reference clock inputs is different depending on the

signaling mode used to connect the clock driver chip and SerDes reference clock inputs as described

below.

•

Differential Mode

— The input amplitude of the differential clock must be between 400 mV and 1600 mV

differential peak-peak (or between 200 mV and 800 mV differential peak). In other words,

each signal wire of the differential pair must have a single-ended swing less than 800 mV and

Input

Amp

n_REF_CLK

MPC8377ECVRAFDA Datasheet(PDF) 79 Page - Freescale Semiconductor, Inc