MPC8544E datasheet(64/117 Pages) FREESCALE

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MPC8544E PowerQUICC III Integrated Processor Hardware Specifications, Rev. 5

Freescale Semiconductor

High-Speed Serial Interfaces (HSSI)

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 SDn_TX, SDn_TX, SDn_RX and

SDn_RX 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: VSDn_TX – VSDn_TX. 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: VSDn_RX – VSDn_RX. 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 (SDn_TX, for

example) from the non-inverting signal (SDn_TX, 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 44 as an example for differential waveform.

7. Common Mode Voltage, Vcm

The Common Mode Voltage is equal to one half of the sum of the voltages between each conductor

of a balanced interchange circuit and ground. In this example, for SerDes output, Vcm_out =

VSDn_TX + VSDn_TX = (A + B) / 2, which is the arithmetic mean of the two complimentary output

voltages within a differential pair. In a system, the common mode voltage may often differ from

one component’s output to the other’s input. Sometimes, it may be even different between the

receiver input and driver output circuits within the same component. It is also referred as the DC

offset in some occasions.

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