WM8742GEDSSLASHV datasheet(20/66 Pages) CIRRUS

20 / 66 page

WM8742

Rev 4.4

of devices in the chain until they are all set into daisy chain mode. Figure 11 shows the protocol for

configuring the first two devices in the daisy chain.

CSB

SCLK

DAC1 SDIN

ADDR=0x08, DATA=0x022

DAC1 SDOUT/

DAC2 SDIN

ADDR=0x08, DATA=0x022

ADDR=0x7F, DATA=0x1FF

DAC1 configured into daisy chain mode

DAC1 receives 16-bits of control data ready to

echo on SDOUT. DAC1 does not act on control

data as no rising CSB to latch data in

DAC1 outputs previous 16-bits of control data on

SDOUT and receives dummy write on SDIN

DAC2 configured into daisy chain mode

Figure 11 Initial Setup of Two WM8742 Devices into Control Interface Daisy Chain Mode

To write to a single device in the chain a complete sequence needs to be written to all the devices.

Devices that do not require a register change must also be written to. The user can choose to write

either the same data as the previous write, or write all 1s for the register address and data. All 1s will

result in writing to a non-existent register, address 7Fh, preserving the current register settings.

Figure 12 shows an example of how to access three WM8742 devices (the devices have all previously

been configured in daisy chain mode):

CSB

SCLK

DAC1 SDIN

DAC1 SDOUT/

DAC2 SDIN

DAC2 SDOUT/

DAC3 SDIN

CSB goes high

DAC1 processes blue data

DAC2 processes yellow data

DAC3 processes pink data

Figure 12 Daisy Chain Control Interface Example for Three WM8742 Devices

To ensure that only valid data is written to the devices in daisy chain mode, a pull up resistor is used

in SDOUT. When connected to the SDIN pin of the next device in the chain, this results in all ones

being written to the control interface of that device until the correct daisy chain data is written and

latched.

Serial daisy chaining is available only when using 3-wire serial control mode. It is not available in 2-

wire serial control mode or hardware control mode.

BIT

LABEL

DEFAULT

DESCRIPTION

Mode Control 2

08h

SDOUT

3 wire Serial Interface Daisy Chaining

0 = No Output

1 = Output on pin 25.

Table 9 Control Interface Daisy Chaining Selection

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