PCI Express
Table 62. Differential Receiver (RX) Input Specifications (continued)
Symbol
Parameter
Total Skew
Min Nominal
Max
Units
Comments
L
—
—
20
ns
Skew across all lanes on a Link. This
includes variation in the length of SKP
ordered set (for example, COM and one to
five SKP Symbols) at the RX as well as any
delay differences arising from the
interconnect itself.
RX-SKEW
Notes:
1. No test load is necessarily associated with this value.
2. Specified at the measurement point and measured over any 250 consecutive UIs. The test load in Figure 57 should be used
as the RX device when taking measurements (also refer to the Receiver compliance eye diagram shown in Figure 56). If the
clocks to the RX and TX are not derived from the same reference clock, the TX UI recovered from 3500 consecutive UI must
be used as a reference for the eye diagram.
3. A T
= 0.40 UI provides for a total sum of 0.60 UI deterministic and random jitter budget for the Transmitter and
RX-EYE
interconnect collected any 250 consecutive UIs. The T
specification ensures a jitter distribution
RX-EYE-MEDIAN-to-MAX-JITTER
in which the median and the maximum deviation from the median is less than half of the total. UI jitter budget collected over
any 250 consecutive TX UIs. It should be noted that the median is not the same as the mean. The jitter median describes the
point in time where the number of jitter points on either side is approximately equal as opposed to the averaged time value.
If the clocks to the RX and TX are not derived from the same reference clock, the TX UI recovered from 3500 consecutive UI
must be used as the reference for the eye diagram.
4. The Receiver input impedance shall result in a differential return loss greater than or equal to 15 dB with the D+ line biased
to 300 mV and the D- line biased to -300 mV and a common mode return loss greater than or equal to 6 dB (no bias required)
over a frequency range of 50 MHz to 1.25 GHz. This input impedance requirement applies to all valid input levels. The
reference impedance for return loss measurements for is 50 ohms to ground for both the D+ and D- line (that is, as measured
by a Vector Network Analyzer with 50 ohm probes - see Figure 57). Note: that the series capacitors CTX is optional for the
return loss measurement.
5. Impedance during all LTSSM states. When transitioning from a Fundamental Reset to Detect (the initial state of the LTSSM)
there is a 5 ms transition time before Receiver termination values must be met on all un-configured Lanes of a Port.
6. The RX DC Common Mode Impedance that exists when no power is present or Fundamental Reset is asserted. This helps
ensure that the Receiver Detect circuit does not falsely assume a Receiver is powered on when it is not. This term must be
measured at 300 mV above the RX ground.
7. It is recommended that the recovered TX UI is calculated using all edges in the 3500 consecutive UI interval with a fit algorithm
using a minimization merit function. Least squares and median deviation fits have worked well with experimental and
simulated data.
MPC8572E PowerQUICC III Integrated Processor Hardware Specifications, Rev. 4
88
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