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MSC8144E Quad Core Digital Signal Processor Data Sheet, Rev. 6

Electrical Characteristics

Freescale Semiconductor

2.7.5.2

Signal Definitions

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

signals. Figure 12 shows how the signals are defined. The figure shows waveforms for either a transmitter output (TD and TD)

or a receiver input (RD and RD). Each signal swings between voltage levels A and B, where A > B.

Note:

This explanation uses generic TD/TD/RD/RD signal names. These correspond to SRIO_TXD/SRIO_TXD/

SRIO_RXD/SRIO_RXD respectively.

Using these waveforms, the definitions are as follows:

The transmitter output signals and the receiver input signals TD, TD, RD and RD each have a peak-to-peak voltage

(VPP) swing of A – B.

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

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

The differential output signal of the transmitter and the differential input signal of the receiver each range from A – B

to –(A – B).

The peak value of the differential transmitter output signal and the differential receiver input signal is A – B.

The value of the differential transmitter output signal and the differential receiver input signal is 2

× (A – B) V

PP.

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 V and 2.0 V. Using these values,

the peak-to-peak voltage swing of the signals TD and TD is 500 mVPP. The differential output signal ranges between 500 mV

and –500 mV. The peak differential voltage is 500 mV. The peak-to-peak differential voltage is 1000 mVPP.

Note:

AC electrical specifications are given for transmitter and receiver. Long run and short run interfaces at three baud

rates (a total of six cases) are described. The parameters for the AC electrical specifications are guided by the XAUI

electrical interface specified in Clause 47 of IEEE™ Std 802.3ae-2002™. XAUI has similar application goals to

serial RapidIO. The goal of this standard is that electrical designs for serial RapidIO can reuse electrical designs for

XAUI, suitably modified for applications at the baud intervals and reaches described herein.

2.7.5.3

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.

Figure 12. Differential VPP of Transmitter or Receiver

Differential Peak-Peak = 2

× (A – B)

TD or RD

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