MPC8308 datasheet(39/90 Pages) FREESCALE

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MPC8308 PowerQUICC II Pro Processor Hardware Specification, Rev. 2

Freescale Semiconductor

PCI Express

11.4.2

Transmitter Compliance Eye Diagrams

The TX eye diagram in Figure 27 is specified using the passive compliance/test measurement load

(Figure 29) in place of any real PCI Express interconnect + RX component. There are two eye diagrams

that must be met for the transmitter. Both diagrams must be aligned in time using the jitter median to locate

the center of the eye diagram. The different eye diagrams differ in voltage depending on whether it is a

transition bit or a de-emphasized bit. The exact reduced voltage level of the de-emphasized bit is always

relative to the transition bit.

The eye diagram must be valid for any 250 consecutive UIs.

A recovered TX UI is calculated over 3500 consecutive unit intervals of sample data. The eye diagram is

created using all edges of the 250 consecutive UI in the center of the 3500 UI used for calculating the TX

UI.

NOTE

It is recommended that the recovered TX UI be calculated using all edges in

the 3500 consecutive UI interval with a fit algorithm using a minimization

merit function (that is, least squares and median deviation fits).

Crosslink random timeout

Tcrosslink

This random timeout helps

resolve conflicts in

crosslink configuration by

eventually resulting in only

one Downstream and one

Upstream Port.

0—

Notes:

1. No test load is necessarily associated with this value.

2. Specified at the measurement point into a timing and voltage compliance test load as shown in Figure 29 and measured over

any 250 consecutive TX UIs. (Also refer to the transmitter compliance eye diagram shown in Figure 27.)

3. A TTX-EYE = 0.70 UI provides for a total sum of deterministic and random jitter budget of TTX-JITTER-MAX = 0.30 UI for the

transmitter collected over any 250 consecutive TX UIs. The TTX-EYE-MEDIAN-to-MAX-JITTER median is less than half of the total

TX 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.

4. The transmitter input impedance shall result in a differential return loss greater than or equal to 12 dB and a common mode

return loss greater than or equal to 6 dB 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 is 50

Ω to ground for both the D+ and

D– line (that is, as measured by a vector network analyzer with 50-

Ω probes, see Figure 29). Note that the series capacitors,

CTX, is optional for the return loss measurement.

5. Measured between 20%–80% at transmitter package pins into a test load as shown in Figure 29 for both VTX-D+ and VTX-D-.

6. See Section 4.3.1.8 of the

PCI Express Base Specifications, Rev 1.0a.

7. See Section 4.2.6.3 of the

PCI Express Base Specifications, Rev 1.0a.

Table 34. Differential Transmitter (TX) Output Specifications (continued)

Parameter

Symbol

Comments

Min

Typical

Max

Units

Notes

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