CM6571 Datasheet, PDF (40/63 Pages) C-Media Electronics – USB 2.0 full speed-compliant

CM6571
USB Audio Sound Chip
The number of subframes that are used depends on the number of channels that are transmitted. A CD player uses
channels A and B (left/right), so each frame contains two subframes. A block contains 192 frames and starts with
the preamble B:
Sub-frame
0
34
78
Preamble Aux Data
LSB
Audio Data
V: valid, U: user data, C: channel-status data, P: parity bit
SPDIF Sub-frame Description
27 28 29 30 31
MSB
VUCP
In each block, 384 bits of channel status and subcode info are transmitted. The channel-status bits are equal for both
subframes, so only 192 useful bits are transmitted:
M ChannelA W ChannelA B ChannelA W ChannelA M ChannelA W ChannelA
Frame 191
SubFrame SubFrame
Frame 0
Frame 1
192-bit SPDIF Frame Preamble Description Diagram
8.7.2 SPDIF out channel status
Bit 0
Bit 1
Bit 2
Bit 3
Bit 4
Bit 5
Bit 6
Bit 7
Byte 0
Consumer
/Professional
Audio/
Non-audio
Copyright
Pre-emphasis
Mode
Default
Byte 1
Default
Byte 2
Default
Byte 3
Default
0 (P)
0 (P)
0 (fixed)
0 (P)
0 (P)
1 (P)
0 (P)
Category Code
0 (P)
0 (P)
0(P)
source number
0 (fixed) 0 (fixed) 0 (fixed)
Sampling Frequency
0 (P)
0 (P)
0 (P)
0 (fixed) 0 (fixed) 0 (fixed) 0 (fixed)
L
0 (P)
0 (P)
0 (P)
0 (P)
Channel Number
0 (fixed) 0 (fixed) 0 (fixed) 0 (fixed)
Clock Accuracy
Reserved
0 (fixed) 0 (fixed) 0 (fixed) 0 (fixed)
Note: P bit can be programmed by USB HID or USB vendor command
Revised: Nov. 2012
Page 40 / 63
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