GS2972 Datasheet, PDF (49/125 Pages) Semtech Corporation – 3G/HD/SD-SDI Serializer with Complete SMPTE Audio & Video Support

4.7.3 3G Mode
When the GS2972 is operating in 3G mode, 8 channels of audio in 4 pairs can be
embedded in the serial output signal, according to SMPTE ST 299.
The 8 channels are in 2 groups, which are selectable via the host interface from the four
groups allowed by SMPTE ST 299. The default is Group One and Group Two.
SMPTE ST 425 describes different mappings for the video signal, each with its own
locations for audio data and control packets:
4.7.3.1 Level A Signals:
SMPTE ST 425 Level A describes a single video signal carried in a 3G bit stream.
The bit stream is made of two multiplexed virtual streams, Data Stream One and Data
Stream Two.
Data Stream One carries audio control packets in the same way that the Y channel
carries audio control packets in SMPTE ST 292 HD signals, but at twice the rate.
Data Stream Two carries audio data packets in the same way that the C channel carries
audio data packets in SMPTE ST 292 HD signals, but at twice the rate.
For Level A signals with mappings 2 (1080i/p, 720p 4:4:4 10-bit), 3 (1080i/p 4:4:4 12-bit)
or 4 (1080i/p, 720p 4:2:2 12-bit), the audio data packets are embedded at the full rate of
148.5MHz, but the clock phase bits are calculated assuming the original PCLK signal of
74.25MHz. This factor of two must be taken into consideration when calculating the
clock bits.
SMPTE ST 425 requires SMPTE ST 352 payload packets to be embedded in both Data
Stream One and Data Stream Two.
4.7.3.2 Level B Signals:
SMPTE ST 425 Level B describes the carriage of two SMPTE ST 292 signals in a single 3G
bit stream. It also applies to a SMPTE ST 372 dual link signal.
The two signals are designated Link A and Link B. Each can carry audio data in the same
way that a SMPTE ST 292 bit stream carries audio data.
The GS2972 is capable of embedding audio data onto either Link A or Link B of the Level
B signal. The default will be Link A.
Link A and Link B are presented to the GS2972 as 10-bit signals at a 148.5MHz PCLK rate.
4.7.4 HD Mode
When the GS2972 is operating in HD mode, 8 channels of audio in 4 pairs are embedded
in the serial output signal, according to SMPTE ST 299.
The 8 channels will be in 2 groups, which are selectable via the host interface from the 4
groups allowed by SMPTE ST 299. The default group is Group One and Group Two.
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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