WM9707
Advanced Information
There is no provision for pseudo-stereo effects. Mono signals will have no enhancement applied
(if the signals are in phase and of the same amplitude).
Signals from the PCM DAC channels can have stereo enhancement applied. It can also be bypassed
if desired. This control is enabled by setting the POP bit in Register 20h.
VARIABLE SAMPLE RATE SUPPORT
The DACs and ADCs on this device support all the recommended sample rates specified in the Intel
Revision 2.1 specification for audio rates. The default rate is 48ks/s. If alternative rates are selected
and variable rate audio is enabled (Register 2Ah, bit 0), 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 Revision 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.
The left and right channels of the ADCs and DACs always sample at the same rate.
AUDIO
SAMPLE RATE
CONTROL VALUE
D15-D0
1F40
8000
11025
16000
22050
44100
48000
2B11
3E80
5622
AC44
BB80
Table 1 Variable Sample Rates Supported
SPDIF DIGITAL AUDIO DATA OUTPUT
Pin 48 may be used to output the PCM DAC playback data in SPDIF (IEC958) digital data format. In
order to enable this output, bit SPDF in Register 5Ch should be set or pin 44 pulled high.
Additionally, a bit SCMS in Register 5Ch may also be set, which removes the copyright flag in the
IEC958 data, allowing serial copy protect mechanisms to be implemented. Note that this data output
will only operate at the SYNCH rate and so only supports 48ks/s operation. The PCM DACs continue
to function normally when SPDIF output is enabled.
GAIN CONTROL REGISTER LOCATION
PGA
CONTROL REGISTER
MUTE DEFAULT
Muted (bit-15)
Not-muted (bit-15)
Muted (15)
DAC
Mixer
18h
72h
02h
Volume
Table 2 Gain Control Register Location
MASTER/SLAVE ID SUPPORT
WM9707 supports operation as either a master or a slave codec. Configuration of the device as
either a master or as a slave, is selected by tying the CID pin 45 on the package.
Fundamentally, a device identified as a master (ID = 0) produces BITCLK as an output, whereas a
slave (any other ID) must be provided with BITCLK as an input. This has the obvious implication that
if the master device on an AC link is disabled, the slave devices cannot function.
The AC’97 Revision 2.1 specification defines that the CID pin has inverting sense, and are provided
with internal weak pull ups. Therefore, if no connections are made to the CID pin, then the pin pulls hi
and an ID = 0 is selected, i.e. master. External connects to ground will select other IDs.
WOLFSON MICROELECTRONICS LTD
AI Rev 2.2 January 2001
12
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
