lm4543 National Semiconductor Corporation, lm4543 Datasheet - Page 12

• Manufacturer Part Number: lm4543
• Description: Ac ?97 Codec With National 3d Sound
• Manufacturer: National Semiconductor Corporation

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Application Information
AC Link Serial Interface Protocol
AC Link Output Frame
The audio output frame (output from AC ’97 Controller) con-
tains control and PCM data targeted for the LM4543 control
registers and stereo DAC. The Tag slot, slot 0, contains 16
bits that tell the AC Link interface circuitry on the LM4543 the
validity of the following data slots.
A new audio output frame is signaled with a low to high tran-
sition of SYNC. SYNC is synchronous to the rising edge of
BIT_CLK. On the next rising edge of BIT_CLK, the AC ’97
Controller drives SD_OUT with the first bit of slot 0. The
LM4543 samples SD_OUT on the falling edge of BIT_CLK.
The AC ’97 Controller will continue outputting the SD_OUT
stream on each successive rising edge of BIT_CLK.
SD_OUT Slot 0: Tag Phase
The first bit of slot 0 is designated the Valid Frame bit. If
this bit is 1, it indicates that the current data frame contains
at least one slot of valid data and the LM4543 will further
sampled the next four bits to determine which frames do in
fact have valid data. Valid slots are signified by a 1 in their re-
spective slot bit position.
FIGURE 3. AC 97 Bidirectional Audio Frame
FIGURE 4. AC Link Audio Output Frame
12
Bit
15
14
13
12
FIGURE 5. Start of Audio Output Frame
Left Playback
register data
Description
Valid Frame
PCM Data
address
register
Control
Control
1 = Valid Frame
1 = Valid slot
1 = Valid slot
1 = Valid slot
Comment
DS100907-4
DS100907-6
DS100907-5