WM8756

Advance Information

AI Rev 1.3 October 2001

18

SOFTWARE CONTROL MODES

DIGITAL AUDIO INTERFACE CONTROL REGISTERS

Interface format is selected via the FMT[1:0] register bits:

REGISTER ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

0000011

Interface Control

1:0

FMT[1:0]

00

Interface format Select

00 : right justified mode

01: left justified mode

10: I2S mode

11: DSP (early or late) mode

In left justified, right justified or I2S modes, the LRP register bit controls the polarity of LRCIN. If this bit is

set high, the expected polarity of LRCIN will be the opposite of that shown in Figure 6, Figure 7 and

Figure 8. Note that if this feature is used as a means of swapping the left and right channels, a 1 sample

phase difference will be introduced.

REGISTER ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

0000011

Interface Control

2

LRP

0

LRCIN Polarity

0 : normal LRCIN polarity

1: inverted LRCIN polarity

In DSP modes, the LRCIN register bit is used to select between early and late modes:

REGISTER ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

0000011

Interface Control

2

LRP

0

DSP Format

0 : Early DSP mode

1: Late DSP mode

By default, LRCIN and DIN0/1/2 are sampled on the rising edge of BCKIN and should ideally change on

the falling edge. Data sources which change LRCIN and DIN0/1/2 on the rising edge of BCKIN can be

supported by setting the BCP register bit. Setting BCP to 1 inverts the polarity of BCKIN to the inverse of

that shown in Figures 6, 7 and 8.

REGISTER ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

0000011

Interface Control

3

BCP

0

BCKIN Polarity

0 : normal BCKIN polarity

1: inverted BCKIN polarity

The IWL[1:0] bits are used to control the input word length.

REGISTER ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

0000011

Interface Control

5:4

IWL[1:0]

10

Input Word Length

00 : 16 bit data

01: 20 bit data

10: 24 bit data

11: 32 bit data

Note: If 32-bit mode is selected in right justified mode, the WM8756 defaults to 24 bits.

In all modes, the data is signed 2's complement. The digital filters always input 24-bit data. If the DAC is

programmed to receive 16 or 20 bit data, the WM8756 pads the unused LSBs with zeros. If the DAC is

programmed into 32 bit mode, the 8 LSBs are ignored.