WM8731L WOLFSON [Wolfson Microelectronics plc], WM8731L Datasheet - Page 37

• Manufacturer Part Number: WM8731L
• Description: Portable Internet Audio CODEC with Headphone Driver and Programmable Sample Rates
• Manufacturer: WOLFSON [Wolfson Microelectronics plc]

WM8731 / WM8731L
Figure 30 DSP/PCM Mode Audio Interface (mode B, LRP=0)
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In all modes DACLRC and ADCLRC must always change on the falling edge of BCLK, refer to Figure
26, Figure 27, Figure 28,
Figure 29 and Figure 30.
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,
I
ratios need more careful consideration.
In Slave mode, DACLRC and ADCLRC 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/ADCLRC transition to clock the chosen data word length. The non-50:50 requirement
on the LRCs 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 LRCs and BCLK will not generate the appropriate
DACLRC or ADCLRC since they 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/ADCLRC can
be made non 50:50.
In Master mode, DACLRC and ADCLRC will be output with a 50:50 mark-space ratio with BCLK
output at 64 x base frequency (i.e. 48 kHz).. The exception again is in USB mode where BCLK is
always 12MHz. So for example in 12MHz/32k fs mode there are 375 master clocks per DACLRC
period. Therefore DACLRC and ADCLRC outputs will have a mark space ratio of 187:188.
The ADC and DAC digital audio interface modes are software configurable as indicated in Table 14.
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, in I2S or left justified
modes only. Refer to the software control table below. The data is signed 2’s complement. Both ADC
and DAC are fixed at the same data length. The ADC and DAC digital filters process data using 24
bits. If the ADC is programmed to output 16 or 20 bit data then it strips the LSBs from the 24 bit data.
If the ADC is programmed to output 32 bits then it packs the LSBs with zeros. If the DAC is
programmed to receive 16 or 20 bit data, the WM8731/L 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 15. Stereo samples are normally generated as a Left/Right sampled pair. LRSWAP reverses
the order so 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.
2
S and Right Justified), the DACLRC, ADCLRC and BCLK frequencies, continuity and mark-space
PD Rev 4.3 August 2006
Production Data
37