cx25840 Conexant Systems, Inc., cx25840 Datasheet - Page 16

• Manufacturer Part Number: cx25840
• Description: Video Decoder And Broadcast Audio
• Manufacturer: Conexant Systems, Inc.

Functional Overview
1.1.1.8
1.1.2
1.1.2.1
1.1.2.2
1-4
Audio Features
Vertical Blanking Interval Data Slicing and Decoding
An integrated VBI data slicer supports a variety of data standards: WST, Closed
Caption, WSS, VITC, as well as programming guide information like Gemstar 1x,
Gemstar 2x, and VPS. Decoded data for closed caption, WSS, and Gemstar services is
available through either a register read or can be inserted as ancillary data within the
ITU-R BT.656 data stream. For high-bit rate services such as WST, NABTS, VPS,
and VITC, data is provided on the pixel output port and can be inserted as ancillary
data as well. There is independent control of what data service is to be sliced/decoded
for every line of each field in the vertical interval. Programmability is also provided
such that custom data slicing can be accomplished for data services that do not
comply with one of the standards already supported.
Stereo Broadcast Audio Decoding
The CX25843, CX25842, CX25841, and CX25840 integrate a stereo broadcast audio
decoder capable of demodulating all of the most common worldwide audio standards:
BTSC, EIAJ, A2, NICAM, FM (standard and high-deviation modes), and AM. The
sound IF output from the tuner interfaces directly with the CX25840/1/2/3,
eliminating the need for external sound demodulation chips. Dual language,
subchannel, and Secondary Audio Formats (SAP) are also supported for broadcasts
that transmit multilingual capability. Simultaneous dual language can be supported
with different languages on each channel of the stereo left/right pair. The audio
decoder has automatic standard detection and configuration through an on-board
microprocessor so that no user intervention is necessary to set up the decoder for the
various standards. This is especially useful in geographic regions where different
audio standards may be received on a channel-by-channel basis.
Audio Interfaces
Demodulated broadcast audio is available through two interfaces, serial audio output
or embedded in the ITU-R BT.656/VIP pixel port as ancillary data. The serial audio
output port can supply audio samples from the broadcast decoder or from the serial
audio input port. An internal sample rate converter allows for selection of 32 kHz,
44.1 kHz, 48 kHz, or 96 kHz sample rate for easy system integration. This sample rate
conversion is available for both the serial audio (input and output) and BT.656/VIP
interfaces, independent of one another. In the BT.656/VIP mode, audio samples are
embedded into the video stream and are tagged as ancillary data during the horizontal
blanking interval. This allows for the capture of audio samples on systems that do not
provide serial audio interfaces. The CX25840/1/2/3 also provides a serial audio input
and an AC’97 link interface for extensible baseband audio capture and playback.
Adding an AC’97 audio codec provides support for multiple audio inputs and outputs
for systems that require a broad range of audio interfaces. The serial audio interfaces
support programmable master/slave modes and 16- to 32-bit sample widths.
Conexant
CX25840/1/2/3 Data Sheet
102284B
8/3/05