WM9704M Datasheet, PDF (14/37 Pages) Wolfson Microelectronics plc – AMC97 Audio and Modem Codec

WM9704M
Production Data
VARIABLE SAMPLE RATE SUPPORT
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.
AUDIO
SAMPLE RATE
CONTROL VALUE
D15 TO D0
8000
11025
16000
22050
44100
48000
1F40
2B11
3E80
5622
AC44
BB80
Table 2 Variable Sample Rates Supported
MODEM
SAMPLE RATE
7200
8228.57 (57600/7)
8400
9000
9600
10285.71 (72000/7)
12000
13714.28 (96000/7)
19200
24000
CONTROL VALUE
D15 TO D0
1C20
2024
20D0
2328
2580
282D
2EE0
3592
4B00
5DC0
The following table shows which registers control which DAC rates, versus Mode and ID selected
MODE
ID
FRONT DAC RATE REGISTER
Rev 2.1 mode (00)
Modem mode (11)
00 and 01
10
11
00 and 01
10
11
2Ch
2Eh
2Ch (centre) and 30h (LFE)
2Ch
2Eh
2Ch (centre) and 30h (LFE)
Table 3 Variable Rate Register Location Versus Mode and ID
REAR DAC RATE REGISTER
40h
ADC RATE
REG
32h
32h (40h if
PHONE
IP selected)
GAIN CONTROL REGISTER LOCATION VERSUS MODE AND ID
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.
WOLFSON MICROELECTRONICS LTD
PD Rev 3.2 January 2001
14