LM4540VH National Semiconductor, LM4540VH Datasheet - Page 12

• Manufacturer Part Number: LM4540VH
• Description: IC AUDIO CODEC '97 18BIT 48LQFP
• Manufacturer: National Semiconductor
• Type: Audio Codec '97r

Specifications of LM4540VH

• Data Interface: Serial
• Resolution (bits): 18 b
• Number Of Adcs / Dacs: 2 / 2
• Sigma Delta: Yes
• Dynamic Range, Adcs / Dacs (db) Typ: 90 / 89
• Voltage - Supply, Analog: 4.2 V ~ 5.5 V
• Voltage - Supply, Digital: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 48-LQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *LM4540VH

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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 LM4540 control
registers and stereo DAC. The Tag slot, slot 0, contains 16
bits that tell the AC Link interface circuitry on the LM4540 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
LM4540 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 LM4540 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
DS100906-4
DS100906-6
DS100906-5