WM8740

Production Data

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PD, Rev 4.4, April 2010

19

SOFTWARE DIFFERENTIAL MONO MODE

To control the WM8740 in software differential mode register M4 must be written to. A ‘key’ register

write must be made to register M2 to allow access to register M4 which is ‘locked’ as default. Bits B5

to B8 of register M2 must be set to ‘1’ (0x01e0).

With register M4 ‘unlocked’, bits B4 and B5 may be used to set the required differential output mode;

normal stereo, reversed stereo, mono left or mono right, as shown in Table 18.

DIFF[1:0]

B[5:4])

DIFFERENTIAL OUTPUT MODE

00

Stereo

10

Stereo reverse.

01

Mono left – differential outputs.

VOUTLP (17) is left channel.

VOUTLN (16) is left channel inverted.

VOUTRP (12) is left channel inverted.

VOUTRN (13) is left channel.

11

Mono right – differential outputs.

VOUTLP (17) is right channel inverted.

VOUTLN (16) is right channel.

VOUTRP (12) is right channel.

VOUTRN (13) is right channel inverted.

Table 18 Differential Output Modes

Using these controls a pair of WM8740 devices may be used to build a dual differential stereo

implementation with higher performance and differential output.

Note: DIFFHW mode pin may be used to achieve the same result by hardware means.

CLOCK LOSS DETECTOR DISABLE

CDD (REG4, B6)

L

Clock loss detector on

R

Clock loss detector off

Table 19 Clock Loss Detector Disable

When the system clock is inactive for approximately 100

μs, the clock loss detector circuit detects the

loss of clock and the analogue circuitry is forced into a mute condition and the digital filters reset.

Setting the CDD bit disables this behaviour.