GS9023A 查看數據表（PDF） - Gennum -> Semtech
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GS9023A Datasheet PDF : 37 Pages
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2.1.7 Audio Data Packets
The GS9023A can multiplex up to four audio channels. The
channels are selectable via the “CHACT(4-1)” bits of Host
Interface Register #1h. The audio group (Audio packet data
ID) for each device is configured in “AD20ID[3:0]” of Host
Interface Register #3h. On power up, the four audio
channels and audio group 1 are selected by default.
By setting all the “CHACT(4-1)” bits in Host Interface
Register #1h to zero, the GS9023A will be in bypass mode
whereby any existing audio data packets, with the same
audio group ID or otherwise, will pass through the device
unchanged and no new audio data packets will be
embedded.
NOTE: Do not rely on default value. Reprogram on power
up or reset.
The “CASCADE” bit in Host Interface Register #4h controls
the manner in which multiplexing is performed. When
“CASCADE” is LOW, the GS9023A deletes all existing
ancillary packets. New packets are multiplexed at the first
location after the end of active video (EAV) in the horizontal
ancillary space (HANC). See Figure 2.
When “CASCADE” is HIGH, the GS9023A multiplexes
packets at the first free location in the horizontal ancillary
(HANC) space after the end of active video (EAV) if there is
sufficient space remaining to insert the packet. The
GS9023A does not check if existing audio group samples
are present in the video signal. Use caution in applications
where the video signal contains existing audio packets to
avoid adding identical group samples. See Figure 3.
The GS9023A assumes that the ancillary space from the
first free location is empty to the start of active video (SAV).
Existing ancillary data packets (inserted by previous
devices) in the video signal must be contiguous from the
beginning of the HANC space or the insertion of a new
audio data packet may overwrite existing data. See Figure
4.
Video Signal before GS9023A
Empty
Empty
Video Signal after GS9023A Insertion of Audio Group 1 ("CASCADE" = LOW)
Figure 2
GENNUM CORPORATION
Video Signal before GS9023A
Empty
Empty
Video Signal after GS9023A Insertion of Audio Group 3 ("CASCADE" = HIGH)
Figure 3
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