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Audio Codec '97

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AC ‘97 Component Specification Revision 2.3 Rev 1.0
82
6.6.3 Modem Sample Rate Control Registers (Index 40h – 44h)
Reg Name D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 Default
40h Line1 DAC/ADC Rate
(input, output slot 5)
SR15 SR14 SR13 SR12 SR11 SR10 SR9 SR8 SR7 SR6 SR5 SR4 SR3 SR2 SR1 SR0 BB80h
42h Line2 DAC/ADC Rate
(input, output slot 10)
SR15 SR14 SR13 SR12 SR11 SR10 SR9 SR8 SR7 SR6 SR5 SR4 SR3 SR2 SR1 SR0 BB80h
44h Handset DAC/ADC Rate
(input, output slot 11)
SR15 SR14 SR13 SR12 SR11 SR10 SR9 SR8 SR7 SR6 SR5 SR4 SR3 SR2 SR1 SR0 BB80h
For modem AFE, each DAC/ADC pair is governed by a read/write modem sample rate control register that contains
a 16-bit unsigned value between 0 and 65535, representing the rate of operation in Hz. Any number written over
BB80h will cause the sample rate to be 48 kHz. For all rates, if the value written to the register is supported, that
value will be echoed back when read; otherwise the closest (higher in case of a tie) rate supported is returned.
Table 42 defines the recommended set of sample rates for consideration. Although bit fields could be used to
support the relatively few recommended sample rates, a full 16-bit register was chosen as the most flexible way to
support future expandability.
Support for the non-integer sample rates, 13,714.28 (96000/7), 8228.57 (57600/7), and 10285.71 (72000/7), requires
that the Codec automatically recognize the non-integer rate from the integer portion.
Recommended (+) sample rates for modem AFE (Hz)
Sample rate D15-D0 line1, line2 handset
7200 1C20 +
8000 1F40 + +
8228.57 (57600/7) 2024 +
8400 20D0 +
9000 2328 +
9600 2580 +
10285.71 (72000/7) 282D +
12000 2EE0 +
13,714.28 (96000/7) 3592 +
16000 3E80 + +
19200 4B00 +
Table 42. Sample Rates for Modem AFE (Hz)
Note: To comply with ITU-T modem recommendations, sample rates must be generated to a tolerance of +/- 0.01%.
This includes crystal tolerance, including variations over voltage, temperature, and age.
The default value after cold or register reset for these registers (BB80h) is 48 kHz.