GS3471 datasheet(29/179 Pages) SEMTECH

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GS3471

Final Data Sheet Rev.4

PDS-060498

September 2017

29 of 179

Semtech

www.semtech.com

4.4.2 Low Latency Video Path

The GS3471 has a low latency mode of operation for audio and ancillary data extraction.

Audio can be extracted without incurring any associated delay if the error correction

feature and audio packet delete feature are not required. The device will automatically

select low latency mode if the ALL_DEL CSR bit is set LOW (SD) or ALL_DEL CSR bit is

set LOW and ECC_OFF CSR bit is set HIGH (HD/3G). This means that in low latency mode

for audio, ECC errors in the HD/3G audio data packets will not be corrected and no audio

packets will be deleted from the data stream after extraction. If either of these features

are desired, then a delay will be incurred through the audio extraction blocks. To

maintain consistent delay independent of selected features, the

LOW_LATENCY_BYPASS bit must be set HIGH.

Ancillary data will automatically be extracted without incurring any associated delay if

the ANC_DATA_DEL CSR bit is set LOW.

4.4.3 SMPTE and SMPTE Bypass Mode

The GS3471 has the ability to run either in SMPTE mode or SMTPE Bypass mode.

In SMPTE mode (SMPTE_BYPASS = HIGH), the timing signal generator becomes

operational, video signals error detection and SMPTE processing functions are available,

and the retimer PLL locks to valid SMPTE video.

In SMPTE Bypass mode (SMPTE_BYPASS = LOW), the GS3471 operates either in

DVB-ASI mode or Data-Through mode. When operating in SMPTE Bypass mode, none of

the SMPTE detection and processing functions are available.

4.4.3.1 Descrambling and Word Alignment

The GS3471 performs NRZI (Non Return to Zero Invert) to NRZ (Non Return to Zero)

decoding and data descrambling according to SMPTE ST 424/SMPTE ST 292/SMPTE ST

259-C and word aligns the data to TRS sync words.

When operating in Manual mode (AUTO_MAN = LOW), the device only carries out

SMPTE decoding, descrambling, and word alignment, when the SMPTE_BYPASS bit is

set HIGH and the DVB_ASI bit is set LOW.

When operating in Auto mode (AUTO_MAN = HIGH), the GS3471 carries out

descrambling and word alignment to enable the detection of TRS sync words. When

two consecutive valid TRS words (SAV and EAV), with the same bit alignment have been

detected, the device word-aligns the data to the TRS ID words.

TRS ID word detection is a continuous process. The device remains in SMPTE mode until

TRS ID words fail to be detected.

Note 1: Both 8-bit and 10-bit TRS headers are identified by the device.

Note 2: In 3G Level B mode, the device only supports Data Stream 1 and Data Stream 2

having the same bit width (i.e. both data streams contain 8-bit data, or both data

streams contain 10-bit data). If the bit widths between the two data streams are

different, the GS3471 cannot word align the input stream. When SMPTE_BYPASS is

HIGH and the device is set to Auto mode, it will continuously try to lock.

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