GS2972 Datasheet, PDF (74/125 Pages) Semtech Corporation – 3G/HD/SD-SDI Serializer with Complete SMPTE Audio & Video Support

4.9.2 3G Format Detection
Format detection is more difficult for 3G signals, as there are two levels of signal (Level
A and Level B) and multiple mappings within each level. Timing information is not
sufficient to fully decode the video format.
For this reason SMPTE ST 352 video payload identifier packets are mandatory for all
SMPTE ST 424 serial signals.
Note: The only exception is when the SMPTE ST 425 mapping is Level B twin
SMPTE ST 292 streams, and one or both of the SMPTE ST 292 streams carries HD-SDTI
data. In this case the HD-SDTI header packets are used for payload identification.
4.9.2.1 Level A and Level B Signals:
The GS2972 uses SMPTE ST 352 packets to determine the video format. The
SMPTE ST 352 packets used for format detection will either be:
• When the 352_INS (address 000h bit 6) bit is LOW, then if either bit 6 or 7 of address
20Ah are HIGH, the format is 3G Level B. If both are LOW, then it will look at the
information programmed at address 00Ah VIDEO_FORMAT_OUT_DS1_X. See
SMPTE ST 425 Standard for details.
• When the bit is HIGH, the format is 3G Level A.
Extraction of SMPTE ST 352 packets cannot be done in 3G Level B.
The GS2972 uses the programmed SMPTE ST 352 packets if the 352_INS register bit in
the IOPROC register is HIGH.
If there are no SMPTE ST 352 packets embedded in the input signal, and the user does
not embed SMPTE ST 352 packets from the host interface, the GS2972 assumes an input
signal of 1080p/50 or 1080p/59.94. The GS2972 uses information from the
RASTER_STRUC_X registers to select between these two frame rates.
For Level B inputs, the GS2972 does not extract the SMPTE ST 352 packets from the
parallel input. The only source of SMPTE ST 352 packets in Level B mode, to be used for
format detection and for embedding in the output data streams, is from the user
programmed registers in the host interface.
Note: If proper SMPTE video is applied and then removed from the input, the device
does not flag that the H_LOCK, V_LOCK, VD_SDT etc. has changed (been lost). This is the
case for either TRS detect or HVF modes. This problem occurs only when the video data
is removed, but not the PCLK. Usually, when a video signal is removed, it includes the
clock, the video data, as well as the H, V, F as a whole. So the scenario is not likely to
occur.
GS2972 3G/HD/SD-SDI Serializer with Complete
SMPTE Audio & Video Support
Final Data Sheet Rev. 9
GENDOC-047479 September 2013
www.semtech.com
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