MPC8313E PowerQUICC II Pro Processor Hardware Specifications, Rev. 4
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Freescale Semiconductor
9
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.
9.1
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 22 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 22 as an example for differential waveform.
7. Common mode voltage, Vcm