Datasheet

MPC8308 PowerQUICC II Pro Processor Hardware Specification, Rev. 3
Freescale Semiconductor 35
PCI Express
11.3 Clocking Dependencies
The ports on the two ends of a link must transmit data at a rate that is within 600 parts per million (ppm)
of each other at all times. This is specified to allow bit rate clock sources with a ±300 ppm tolerance.
11.4 Physical Layer Specifications
Following is a summary of the specifications for the physical layer of PCI Express on this device. For
further details as well as the specifications of the transport and data link layer please use the PCI Express
Base Specification, Rev. 1.0a.
11.4.1 Differential Transmitter (TX) Output
This table defines the specifications for the differential output at all transmitters (TXs). The parameters are
specified at the component pins.
Table 34. Differential Transmitter (TX) Output Specifications
Parameter Symbol Comments Min Typical Max Units Note
Unit interval UI Each U
PETX
is 400 ps ± 300 ppm. U
PETX
does not account for Spread Spectrum
Clock dictated variations.
399.88 400 400.12 ps 1
Differential peak-to-peak
output voltage
V
TX-DIFFp-p
V
PEDPPTX
= 2*|V
TX-D+
- V
TX-D-
| 0.8 — 1.2 V 2
De-Emphasized differential
output voltage (ratio)
V
TX-DE-RATIO
Ratio of the V
PEDPPTX
of the second and
following bits after a transition divided by
the V
PEDPPTX
of the first bit after a
transition.
–3.0 –3.5 –4.0 dB 2
Minimum TX eye width T
TX-EYE
The maximum Transmitter jitter can be
derived as T
TX-MAX-JITTER
= 1 -
U
PEEWTX
= 0.3 UI.
0.70 — — UI 2, 3
Maximum time between the
jitter median and maximum
deviation from the median
T
TX-EYE-MEDIAN-to-
MAX-JITTER
Jitter is defined as the measurement
variation of the crossing points
(V
PEDPPTX
= 0 V) in relation to a
recovered TX UI. A recovered TX UI is
calculated over 3500 consecutive unit
intervals of sample data. Jitter is
measured using all edges of the 250
consecutive UI in the center of the 3500
UI used for calculating the TX UI.
— — 0.15 UI 2, 3
D+/D- TX output rise/fall
time
T
TX-RISE
, T
TX-FALL
— 0.125 — — UI 2, 5
RMS AC peak common
mode output voltage
V
TX-CM-ACp
V
PEACPCMTX
= RMS(|V
TXD+
+ V
TXD-
|/2 -
V
TX-CM-DC
)
V
TX-CM-DC
= DC
(avg)
of |V
TX-D+
+
V
TX-D-
|/2
——20mV2