GX3146 Datasheet, PDF(25/46 Page) Semtech Corporation – Crosspoint Switch with Trace Equalization and Output De-emphasis

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GX3146 Datasheet, PDF (25/46 Pages) Semtech Corporation – Crosspoint Switch with Trace Equalization and Output De-emphasis

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Table 4-4: Tx External Clocks

TX0

EXT_CLK_DIGITAL (AJ35)

EXT_CLK_DIGITAL (AH35)

TX1

EXT_CLK2 (R15)

EXT_CLK2 (T15)

While this facility exists for both TX0 and TX1, the user is cautioned that the digital core

clock is derived from the TX0 data clock, and therefore interface and update timing will

track the external clock frequency if one is provided to TX0.

The pattern generators are enabled by the TX0_PRBS_GEN_ENABLE and

TX1_PRBS_GEN_ENABLE bits (register address 0x802h, bits [1:0] respectively).

The PRBS generating polynomials used are:

1. PRBS7: x7 + x6 + 1

2. PRBS15: x15 + x14 + 1

3. PRBS23: x23 + x18 + 1

The pattern generated is selected via the TX0_PRBS_POLYNOMIAL and

TX1_PRBS_POLYNOMIAL bits (register address 0x800h and 0x801h respectively).

Table 4-5: Generated Patterns

TX0_PRBS_POLYNOMIAL[1:0] (binary)

Pattern Generated

PRBS7

PRBS15

PRBS23

Square Wave

4.6.2 Pattern Checker

The pattern checkers de-serialize incoming serial data before checking for errors in the

parallel domain. Three comparison modes are supported:

1. Neutral Phase Comparison Mode. The incoming data is re-timed in a CDR, and

sampled at the neutral (eye center) phase recovered by the CDR before

de-serialization. Errors with respect to the supported PRBS sequences can be

counted.

2. Offset Phase Comparison Mode. The phase at which the incoming data is

sampled with respect to the recovered clock is adjustable over a full UI. Errors with

respect to the supported PRBS sequences can be counted. By sweeping the

sampling phase and counting errors at each phase, an error rate âbathtub curveâ

can be recorded, and the horizontal eye opening evaluated.

3. Arbitrary Data Comparison Mode. This mode can operate on arbitrary data

patterns. The incoming serial data is sampled at both the neutral phase and the

adjustable phase, and each of the two sampled data streams is de-serialized and the

two streams are compared in the parallel domain.

GX3146 146 x 146 3.5Gb/s Crosspoint

Final Data Sheet Rev. 2

GENDOC-056075 March 2013

www.semtech.com

25 of 46

Proprietary & Confidential

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