lm4546a National Semiconductor Corporation, lm4546a Datasheet - Page 23

• Manufacturer Part Number: lm4546a
• Description: Ac ?97 Rev 2 Multi-channel Audio Codec With Sample Rate Conversion And National 3d Sound
• Manufacturer: National Semiconductor Corporation

Register Descriptions
SAMPLE RATE CONTROL REGISTERS (2Ch, 32h)
These read/write registers are used to set the sample rate
for the left and right channels of the DAC (PCM DAC Rate,
2Ch) and the ADC (PCM ADC Rate, 32h). When Variable
Rate Audio is enabled via bit 0 of the Extended Audio
Control/Status register (2Ah), the sample rates can be pro-
grammed, in 1 Hz increments, to be any value from 4 kHz to
48 kHz. The value required is the hexadecimal representa-
tion of the desired sample rate, e.g. 8000
is a list of the most common sample rates and the corre-
sponding register (hex) values.
VENDOR ID REGISTERS (7Ch – 7Eh)
These two read-only (4E53h, 4350h) registers contain Na-
tional’s Vendor ID and National’s LM45xx codec version
designation. The first 24 bits (4Eh, 53h, 43h) represent the
three ASCII characters “NSC” which is National’s Vendor ID
for Microsoft’s Plug and Play. The last 8 bits are the two
binary coded decimal characters, 4, 6 and identify the codec
to be an LM4546A.
RESERVED REGISTERS
Do not write to reserved registers. In particular, do not write
to registers 24h, 5Ah, 74h and 7Ah. All registers not listed in
the LM4546A Register Map are reserved. Reserved Regis-
ters will return 0000h if read.
Low Power Modes
The LM4546A provides 6 bits to control the powerdown state
of internal analog and digital subsections and clocks. These
SR15:SR0
*BB80h
AC44h
1F40h
3E80h
2B11h
5622h
Common Sample Rates
Sample Rate (Hz)
(Continued)
*48000
16000
22050
44100
10
11025
8000
= 1F40h. Below
23
6 bits (PR0 – PR5) are located in the 8 MSBs of the Pow-
erdown Control/Status register, 26h. The status of the four
main analog subsections is given by the 4 LSBs in the same
register, 26h.
The powerdown bits are implemented in compliance with AC
’97 Rev 2 to support the standard device power manage-
ment states D0 – D3 as defined in the ACPI and PCI Bus
Power Management specification.
PR0 controls the powerdown state of the ADC and associ-
ated sampling rate conversion circuitry. PR1 controls power-
down for the DAC and the DAC sampling rate conversion
circuitry. PR2 powers down the mixer circuits (MIX1, MIX2,
National 3D Sound, Mono Out, Line Out). PR3 powers down
V
powers down the AC Link Digital Interface – see Figure 8 for
signal powerdown timing. PR5 disables internal clocks but
leaves the crystal oscillator and BIT_CLK running (needed
for minimum Primary mode powerdown dissipation in multi-
codec systems). PR6 and PR7 are not used.
After a subsection has undergone a powerdown cycle, the
appropriate status bit(s) in the Powerdown Control/Status
register (26h) must be polled to confirm readiness. In par-
ticular the startup time of the V
value of the decoupling capacitors on pin 27 (3.3 µF, 0.1 µF
in parallel is recommended) and this dependency is behind
the requirement for both PR2 and PR3 functionality in AC ’97
Rev 2.
When the AC Link Digital Interface is powered down the
codec output signals SDATA_IN and BIT_CLK (Primary
mode) are cleared to zero and no control data can be passed
between controller and codec(s). This powerdown state can
be cleared in two ways: Cold Reset (RESET# = 0) or Warm
Reset (SYNC = 1, no BIT_CLK). Cold Reset sets all regis-
ters back to their default values (including clearing PR4)
whereas Warm Reset only clears the PR4 bit and restarts
the AC Link Digital Interface leaving all register contents
otherwise unaffected. For Warm Reset (see Timing Dia-
grams), the SYNC input is used asynchronously. The
LM4546A codec allows the AC Link digital interface power-
down state to be cleared immediately so that its duration can
be essentially as short as T
However for conformance with AC ’97 Rev 2, Warm Reset
should not be applied within 4 frame times of powerdown i.e.
the AC Link powerdown state should be allowed to last at
least 82.8 µs.
REF
in addition to all the same mixer circuits as PR2. PR4
SH
, the Warm Reset pulse width.
REF
circuitry depends on the
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