CS4297A
CS4297A
3.1
AC-Link Serial Data Output Frame
In the serial data output frame, data is passed on the SDATA_OUT pin to the CS4297A from the AC ’97
controller. Figure 9 illustrates the serial port timing.
The PCM playback data being passed to the CS4297A is shifted out MSB first in the most significant bits
of each slot. Any PCM data from the AC ’97 controller that is not 20 bits wide should be left justified in
its corresponding slot and dithered or zero-padded in the unused bit positions.
Bits that are reserved should always be ‘cleared’ by the AC ’97 controller.
3.1.1 Serial Data Output Slot Tags (Slot 0)
Bit 15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Valid Slot 1 Slot 2 Slot 3 Slot 4 Slot 5 Slot 6 Slot 7 Slot 8 Slot 9 Slot 10
Frame Valid Valid Valid Valid Valid Valid Valid Valid Valid Valid
Codec Codec
ID1 ID0
Reserved
Valid Frame
The Valid Frame bit determines if any of the following slots contain either valid playback data
for the CS4297A DACs or data for read/write operations. When ‘set’, at least one of the other
AC-link slots contain valid data. If this bit is ‘clear’, the remainder of the frame is ignored.
Slot [1:2] Valid
Slot [3:10] Valid
The Slot [1:2] Valid bits indicate the validity of data in their corresponding serial data output
slots. If a bit is ‘set’, the corresponding output slot contains valid data. If a bit is ‘cleared’, the
corresponding slot will be ignored.
The Slot [3:10] Valid bits indicate Slot [3:10] contains valid playback data for the CS4297A. If a
Slot Valid bit is ‘set’, the named slot contains valid audio data. If the bit is ‘clear’, the slot will be
ignored. The CS4297A supports alternate slot mapping as defined in the AC ’97 2.1 specifica-
tion. For more information, see the AC Mode Control Register (Index 5Eh).
Codec ID[1:0]
The Codec ID[1:0] bits display the Codec ID of the audio codec being accessed during the cur-
rent AC-link frame. Codec ID[1:0] = 00 indicates the primary codec is being accessed. Codec
ID[1:0] = 01, 10, or 11 indicates one of three possible secondary codecs is being accessed. A
non-zero value of one or more of the Codec ID bits indicates a valid Read or Write Address in
Slot 1, and the Slot 1 R/W bit indicates presence or absence of valid Data in Slot 2.
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DS318PP6
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