wm8742 Wolfson Microelectronics plc, wm8742 Datasheet - Page 34

• Manufacturer Part Number: wm8742
• Description: 24-bit 192khz Dac With Advanced Digital Filtering
• Manufacturer: Wolfson Microelectronics plc

WM8742
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ZERO FLAG OUTPUT
The WM8742 has one zero flag output pin, ZFLAG (pin 21). The zero flag feature is only valid for
PCM data.
The WM8742 asserts Logic 1 on the ZFLAG pin when a sequence of more than 1024 zeros is input to
the chip. The default value is a logical AND of both left and right channels. Under software control,
the user can also set the zero flag pin to respond to either the left channel OR the right channel.
The zero flag pin can be used to control external muting circuits if required.
Table 32 Zero Flag Output
ZFLAG FORCE HIGH CONTROL
It is possible to force the ZFLAG pin to Logic 1 by setting ZFLAG_HI=1 in R7. This is useful in
situations where an application processor may require manual control of an external mute circuit.
Setting ZFLAG_HI=0 will allow the ZFLAG pin to function as defined by ZFLAGLR[1:0].
Table 33 ZFLAG Force High Control
INFINITE ZERO DETECT
The IZD register configures the operation of the WM8742 analogue mute in conjunction with the zero
flag feature. Table 20 shows the interdependency of the MUTEB pin, the IZD register and the zero
flag.
Table 20 Infinite Zero Detect Control
REGISTER ADDRESS
REGISTER ADDRESS
Volume Control
Mode Control 1
Volume Control
REGISTER
ADDRESS
04h
R4
06h
04h
R6
R4
BIT
6:5
BIT
BIT
7
4
ZEROFLR
ZFLAG_HI
LABEL
[1:0]
LABEL
LABEL
IZD
DEFAULT
DEFAULT
DEFAULT
00
0
0
Zero flag output:
00 = Pin assigned to logical AND of
LEFT and RIGHT channels
01 = Pin assigned to LEFT channel
10 = Pin assigned to RIGHT
channel
11 = ZFLAG disabled
ZFLAG Force High Control
0 = Normal operation
1 = Output Logic 1
IZD control of analogue mute:
0 = Never analogue mute
1 = Analogue mute when ZFLAG
set
DESCRIPTION
DESCRIPTION
DESCRIPTION
PD, Rev 4.2,August 2009
Production Data
34