MPC8308VMAFDA datasheet(24/88 Pages) FREESCALE

24 / 88 page

MPC8308 PowerQUICC II Pro Processor Hardware Specification, Rev. 0

Freescale Semiconductor

High-Speed Serial Interfaces (HSSI)

10 High-Speed Serial Interfaces (HSSI)

This section describes the common portion of SerDes DC electrical specifications, which is the DC

requirement for SerDes reference Clocks. The SerDes data lane’s transmitter and receiver reference

circuits are also shown.

10.1

Signal Terms Definition

The SerDes utilizes differential signaling to transfer data across the serial link. This section defines terms

used in the description and specification of differential signals.

Figure 15 shows how the signals are defined. For illustration purpose, only one SerDes lane is used for

description. The figure shows waveform for either a transmitter output (TXn and TXn) or a receiver input

(RXn and RXn). Each signal swings between A Volts and B Volts where A > B.

Using this waveform, the definitions are as follows. To simplify illustration, the following definitions

assume that the SerDes transmitter and receiver operate in a fully symmetrical differential signaling

environment.

1. Single-Ended Swing

The transmitter output signals and the receiver input signals TXn, TXn, RXn and RXn each have

a peak-to-peak swing of A – B Volts. This is also referred as each signal wire’s Single-Ended

Swing.

2. Differential Output Voltage, VOD (or Differential Output Swing):

The Differential Output Voltage (or Swing) of the transmitter, VOD, is defined as the difference of

the two complimentary output voltages: VTXn – VTXn. The VOD value can be either positive or

negative.

3. Differential Input Voltage, VID (or Differential Input Swing):

The Differential Input Voltage (or Swing) of the receiver, VID, is defined as the difference of the

two complimentary input voltages: VRXn – VRXn. The VID value can be either positive or negative.

4. Differential Peak Voltage, VDIFFp

The peak value of the differential transmitter output signal or the differential receiver input signal

is defined as Differential Peak Voltage, VDIFFp = |A – B| Volts.

5. Differential Peak-to-Peak, VDIFFp-p

Since the differential output signal of the transmitter and the differential input signal of the receiver

each range from A – B to –(A – B) Volts, the peak-to-peak value of the differential transmitter

output signal or the differential receiver input signal is defined as Differential Peak-to-Peak

Voltage, VDIFFp-p = 2*VDIFFp = 2 * |(A – B)| Volts, which is twice of differential swing in

amplitude, or twice of the differential peak. For example, the output differential peak-peak voltage

can also be calculated as VTX-DIFFp-p = 2*|VOD|.

6. Differential Waveform

The differential waveform is constructed by subtracting the inverting signal (TXn, for example)

from the non-inverting signal (TXn, for example) within a differential pair. There is only one signal

trace curve in a differential waveform. The voltage represented in the differential waveform is not

referenced to ground. Refer to Figure 24 as an example for differential waveform.

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