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Chapter 2 — Overview and Operation
Both second-channel audio decoders (CS4924 and CS 4931x) are capable of sup-
porting Dolby Digital (AC-3) audio; this feature is not currently supported.
Contact Vela Customer Service regarding Dolby support.
Command Bits
Bit 8
Bits 10–9
Bit 11
Bits 15–12
If an MPEG stream contains only a single MPEG audio track, the IBM audio
decoder will decode it. The secondary audio decoder will remain idle. The audio
switching circuitry can be utilized to output the audio channel on both outputs.
If an MPEG stream contains two MPEG audio tracks, the first stream ID/PID is
sent to the IBM decoder; the second stream ID/PID is sent to the CS49xx audio
decoder.
0038 Video Level (Luma) Adjust: Command ignored by firmware.
0039 Switch Audio: Command ignored by firmware. Refer to command 003C
Set Audio Channel Selection/Audio Fade instead.
003A Set Output Discretes: Each decoder channel has two output discretes for
the user's application. This command provides access to the output discretes. The
output discretes can be configures to switch on a vertical sync.
Command Bits
Bit 8
Bits 9
Function Name
Reserved
Audio Decode Mode
Downmix Mode
Reserved
Function Name
GPOUT1
GPOUT1 Sync
Description
Reserved
00b = Auto mode
01b – 11b = Reserved
0 = Multichannel audio downmixed to
two channels (default).
1 = Multichannel audio played as is
(i.e., not downmixed).
Description
0 = Discrete off (open)
1 = Discrete on (pulled to ground)
0 = Change state immediately
1 = Changes state on Vsync
DECODER Command (45h)
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