MPC8315CVRADDA datasheet(54/106 Pages) FREESCALE

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MPC8315E PowerQUICC II Pro Processor Hardware Specifications, Rev. 2

Freescale Semiconductor

High-Speed Serial Interfaces (HSSI)

•

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 0.4V

(0.4V/50 = 8mA) while the minimum common mode input level is 0.1V above 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 (0-0.8V), such that each phase of the

differential input has a single-ended swing from 0V to 800mV with the common mode voltage

at 400mV.

— If the device driving the SD_REF_CLK and SD_REF_CLK inputs cannot drive 50 ohms to

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 39. Receiver of SerDes Reference Clocks

15.2.2

DC Level Requirement for SerDes Reference Clocks

The DC level requirement for the MPC8315E 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 400mV and 1600mV differential

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

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

200mV. This requirement is the same for both external DC-coupled or AC-coupled connection.

— For external DC-coupled connection, as described in section 15.2.1, the maximum average

current requirements sets the requirement for average voltage (common mode voltage) to be

Input

Amp



SD_REF_CLK

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