WM8711 Wolfson Microelectronics Ltd., WM8711 Datasheet - Page 19

• Manufacturer Part Number: WM8711
• Description: Internet Audio DAC With Integrated Headphone Driver
• Manufacturer: Wolfson Microelectronics Ltd.

WM8711
WOLFSON MICROELECTRONICS LTD
In all modes DACLRC must always change on the falling edge of BCLK, refer to Figure 13, Figure
14, Figure 15 and Figure 16. Operating the digital audio interface in DSP mode allows ease of use
for supporting the various sample rates and word lengths. The only requirement is that all data is
transferred within the correct number of BCLK cycles to suit the chosen word length.
In order for the digital audio interface to offer similar support in the three other modes (Left Justified,
I2S and Right Justified), the DACLRC and BCLK frequencies, continuity and mark-space ratios need
more careful consideration.
In Slave mode, DACLRC inputs are not required to have a 50:50 mark-space ratio. BCLK input need
not be continuous. It is however required that there are sufficient BCLK cycles for each DACLRC
transition to clock the chosen data word length. The non-50:50 requirement on the LRC is of use in
some situations such as with a USB 12MHZ clock. Here simply dividing down a 12MHz clock within
the DSP to generate LRC and BCLK will not generate the appropriate DACLRC since it will no longer
change on the falling edge of BCLK. For example, with 12MHz/32k fs mode there are 375 MCLK per
LRC. In these situations DACLRC can be made non 50:50.
In Master mode, DACLRC will be output with a 50:50 mark-space ratio with BCLK output at 64fs. The
exception is in 96/88.2k mode where BCLK is MCLK and in USB mode where BCLK is always
12MHz. So for example in 12MHz/32k fs mode there are 375 master clocks per LRC period.
Therefore the DACLRC output will have a mark space ratio of 187:188.
The DAC digital audio interface modes are software configurable as indicated in Table 8. Note that
dynamically changing the software format may result in erroneous operation of the interfaces and is
therefore not recommended.
The length of the digital audio data is programmable at 16/20/24 or 32 bits. Refer to the software
control table below. The data is signed 2’s complement. The DAC digital filters process data using 24
bits. If the DAC is programmed to receive 16 or 20 bit data, the WM8711 packs the LSBs with zeros.
If the DAC is programmed to receive 32 bit data, then it strips the LSBs.
The DAC outputs can be swapped under software control using LRP and LRSWAP as shown in
Table 8. Stereo samples are normally generated as a Left/Right sampled pair. LRSWAP reverses
the order of that a Left sample goes to the right DAC output and a Right sample goes to the left DAC
output. LRP swaps the phasing so that a Right/Left sampled pair is expected and preserves the
correct channel phase difference, except in DSP mode, where LRP controls the positioning of the
MSB relative to the rising edge of DACLRC.
To accommodate system timing requirements the interpretation of BCLK maybe inverted, this is
controlled via the software shown in Table 8. This is especially appropriate for DSP mode.
PP Rev 1.2 November 2000
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