MPC8548E datasheet(72/143 Pages) FREESCALE

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MPC8548E PowerQUICC III Integrated Processor Hardware Specifications, Rev. 8

Freescale Semiconductor

PCI Express

17.4.2

Transmitter Compliance Eye Diagrams

The TX eye diagram in Figure 48 is specified using the passive compliance/test measurement load (see

Figure 50) in place of any real PCI Express interconnect +RX component.

There are two eye diagrams that must be met for the transmitter. Both eye 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 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.

ZTX-DIFF-DC

DC differential

TX impedance

100

120

TX DC differential mode low impedance

ZTX-DC

Transmitter DC

impedance

—

Required TX D+ as well as D– DC impedance

during all states

LTX-SKEW

Lane-to-lane

output skew

—

500

+2 UI

Static skew between any two transmitter lanes

within a single Link

CTX

AC coupling

capacitor

—

200

All transmitters shall be AC coupled. The AC

coupling is required either within the media or

within the transmitting component itself. See note

Tcrosslink

Crosslink

random timeout

—

This random timeout helps resolve conflicts in

crosslink configuration by eventually resulting in

only one downstream and one upstream port.

See Note 7.

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 50 and measured over

any 250 consecutive TX UIs. (Also refer to the transmitter compliance eye diagram shown in Figure 48.)

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 50). 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 50 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.

8. MPC8548E SerDes transmitter does not have CTX built in. An external AC coupling capacitor is required.

Table 56. Differential Transmitter (TX) Output Specifications (continued)

Symbol

Parameter

Min

Nom

Max

Unit

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