PPC8567CVTAQGGA datasheet(64/139 Pages) FREESCALE

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MPC8568E/MPC8567E PowerQUICC III Integrated Processor Hardware Specifications, Rev. 1

Freescale Semiconductor

High-Speed Serial Interfaces (HSSI)

Figure 40. Receiver of SerDes Reference Clocks

13.2.2

DC Level Requirement for SerDes Reference Clocks

The DC level requirement for the MPC8568E 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 13.2.1, the maximum average

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

between 100 mV and 400 mV. Figure 41 shows the SerDes reference clock input requirement

for DC-coupled connection scheme.

— For external AC-coupled connection, there is no common mode voltage requirement for the

clock driver. Since the external AC-coupling capacitor blocks the DC level, the clock driver

and the SerDes reference clock receiver operate in different command mode voltages. The

SerDes reference clock receiver in this connection scheme has its common mode voltage set to

SCOREGND. Each signal wire of the differential inputs is allowed to swing below and above

the command mode voltage (SCOREGND). Figure 42 shows the SerDes reference clock input

requirement for AC-coupled connection scheme.

•

Single-ended Mode

— The reference clock can also be single-ended. The SD_REF_CLK input amplitude

(single-ended swing) must be between 400mV and 800mV peak-peak (from Vmin to Vmax)

with SD_REF_CLK either left unconnected or tied to ground.

— The SD_REF_CLK input average voltage must be between 200 and 400 mV. Figure 43 shows

the SerDes reference clock input requirement for single-ended signaling mode.

— To meet the input amplitude requirement, the reference clock inputs might need to be DC or

AC-coupled externally. For the best noise performance, the reference of the clock could be DC

Input

Amp

SD_REF_CLK

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