GS3471 datasheet(84/179 Pages) SEMTECH

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GS3471

Final Data Sheet Rev.4

PDS-060498

September 2017

84 of 179

Semtech

www.semtech.com

4.21.3.2 Detect 5-Frame Sequence Block

Five-frame sequence detection is required for 525-line based video formats only. If the

Audio Frame Number words are set to 200h, the audio de-embedder detects the

five-frame sequence by counting the number of samples per frame. Figure 4-49 shows

the number of samples per frame over a five-frame sequence.

Figure 4-49: Sample Distribution over 5 Video Frames (525-line Systems)

When the audio inputs are asynchronously switched or disrupted, the audio

de-embedder continues to write audio samples into the audio buffer, based on the

current five-frame sequence. The de-embedder then re-locks to the new 5-frame

sequence, at which point a sample may be lost.

Note: In SD, all four channel pairs must follow the same five-frame sequence.

4.21.3.3 Audio FIFO Block

The function of the FIFO block is to change the audio data word rate from the ANC rate

multiplexed with the video signal to the 48kHz audio output rate.

The audio FIFO block contains the audio sample buffers; one per audio channel. Each

buffer is 36 audio samples deep. At power up or reset, the read pointer is held at the zero

position until 26 samples have been written into the FIFO (allows for 6 lines per frame

with no audio samples; a maximum of 4 samples per line in SD mode). See Figure 4-50.

Figure 4-50: Audio Buffer After Initial 26 Sample Write

Frame 1

1602

1601

8008 Samples

1602 Repeat

Audio Buffer

Read

Pointer

Write

Pointer

Address

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