wm9704m Wolfson Microelectronics plc, wm9704m Datasheet - Page 14

• Manufacturer Part Number: wm9704m
• Description: Amc97 Audio Modem Codec
• Manufacturer: Wolfson Microelectronics plc

WM9704M
VARIABLE SAMPLE RATE SUPPORT
Table 3 Variable Rate Register Location Versus Mode and ID
GAIN CONTROL REGISTER LOCATION VERSUS MODE AND ID
WOLFSON MICROELECTRONICS LTD
Rev 2.1 mode (00)
Modem mode (11)
MODE
00 and 01
00 and 01
The DACs and ADCs on this device support all the recommended sample rates specified in the Intel
Rev 2.1 specification for both audio and modem rates. Default rates are 48ks/s. If alternative rates
are selected, the AC’97 interface continues to run at 48k words per second, but data is transferred
across the link in bursts such that the net sample rate selected is achieved. It is up to the AC’97
Rev 2.1 compliant controller to ensure that data is supplied to the AC link, and received from the AC
link, at the appropriate rate.
The device supports ‘on demand’ sampling. That is, when the DAC signal processing circuits need
another sample, a sample request is sent to the controller which must respond with a data sample in
the next frame it sends. For example, if a rate of 24ks/s is selected, on average the device will
request a sample from the controller every other frame, for each of the stereo DACs. Note that if an
unsupported rate is written to one of the rate registers, the rate will default to the nearest rate
supported. The register will then respond when interrogated with the supported rate the device has
defaulted to.
ADCs are controlled similarly but with one difference: Normally the left and right channel ADCs
sample at the same rate.
Table 2 Variable Sample Rates Supported
The following table shows which registers control which DAC rates, versus Mode and ID selected
Depending on what mode and ID the device is operated in, the various gain control registers have
locations in the register map that may change.
In Modem mode, the rear volume is mapped always to location 46h, and the rear mixer is fixed
muted so analogue sources cannot be summed into the Tx modem signal.
ID
10
11
10
11
SAMPLE RATE
AUDIO
11025
16000
22050
44100
48000
8000
FRONT DAC RATE REGISTER
2Ch (centre) and 30h (LFE)
2Ch (centre) and 30h (LFE)
CONTROL VALUE
2Ch
2Eh
2Ch
2Eh
D15 TO D0
AC44
2B11
3E80
BB80
1F40
5622
REAR DAC RATE REGISTER
10285.71 (72000/7)
13714.28 (96000/7)
8228.57 (57600/7)
SAMPLE RATE
MODEM
12000
19200
24000
7200
8400
9000
9600
40h
CONTROL VALUE
PD Rev 3.2 January 2001
D15 TO D0
Production Data
2EE0
5DC0
1C20
20D0
282D
4B00
2024
2328
2580
3592
IP selected)
ADC RATE
32h (40h if
PHONE
REG
32h
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