MPC8548E datasheet(78/144 Pages) FREESCALE

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MPC8548E PowerQUICC™ III Integrated Processor Hardware Specifications, Rev. 6

Freescale Semiconductor

Serial RapidIO

17.3

Signal Definitions

LP-serial links use differential signaling. This section defines terms used in the description and

specification of differential signals. Figure 51 shows how the signals are defined. The figures show

waveforms for either a transmitter output (TD and TD) or a receiver input (RD and RD). Each signal

swings between A volts and B volts where A > B. Using these waveforms, the definitions are as follows:

1. The transmitter output signals and the receiver input signals TD, TD, RD, and RD each have a

peak-to-peak swing of A – B volts.

2. The differential output signal of the transmitter, VOD, is defined as VTD –VTD.

3. The differential input signal of the receiver, VID, is defined as VRD –VRD.

4. The differential output signal of the transmitter and the differential input signal of the receiver

each range from A – B to –(A – B) volts.

5. The peak value of the differential transmitter output signal and the differential receiver input

signal is A – B volts.

6. The peak-to-peak value of the differential transmitter output signal and the differential receiver

input signal is 2

× (A – B) volts.

Figure 51. Differential Peak–Peak Voltage of Transmitter or Receiver

To illustrate these definitions using real values, consider the case of a CML (current mode logic)

transmitter that has a common mode voltage of 2.25 V and each of its outputs, TD and TD, has a swing

that goes between 2.5 and 2.0 V. Using these values, the peak-to-peak voltage swing of the signals TD and

TD is 500 mVp-p. The differential output signal ranges between 500 and –500 mV. The peak differential

voltage is 500 mV. The peak-to-peak differential voltage is 1000 mVp-p.

17.4

Equalization

With the use of high speed serial links, the interconnect media will cause degradation of the signal at the

receiver. Effects such as Inter-Symbol Interference (ISI) or data dependent jitter are produced. This loss

can be large enough to degrade the eye opening at the receiver beyond what is allowed in the specification.

To negate a portion of these effects, equalization can be used. The most common equalization techniques

that can be used are:

•

A passive high pass filter network placed at the receiver. This is often referred to as passive

equalization.

•

The use of active circuits in the receiver. This is often referred to as adaptive equalization.

Differential Peak-to-Peak = 2

× (A – B)

A Volts

TD or RD

B Volts

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