WM8728

Production Data

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PD, Rev 4.6, August 2008

20

SOFTWARE CONTROL INTERFACE

The software control interface may be operated using a 2-wire interface compatible or 3-wire (SPI-

compatible) interface.

SELECTION OF CONTROL MODE

The WM8728 may be programmed to operate in hardware or software control modes. This is

achieved by setting the state of the MODE pin.

MODE

INTERFACE FORMAT

0

Hardware Control Mode

1

Software Control Mode

Table 6 Control Interface Mode Selection

3-WIRE (SPI COMPATIBLE) SERIAL CONTROL MODE

In this mode, SDIDEM is used for the program data, SCK is used to clock in the program data

and LATI2S is used to latch in the program data. The 3-wire interface protocol is shown in Figure

17.

Figure 17 3-Wire Serial Interface

Notes:

1.

B[15:9] are Control Address Bits

2.

B[8:0] are Control Data Bits

3.

CSBIWL needs to be low during writes – see Figure 8

2-WIRE SERIAL CONTROL MODE

In 2-wire mode, which is the default, SDIDEM is used for the program data and SCK is used to

clock in the program data see Figure 18.

WM8728 has an address of 001101X (binary) which represents an audio device. The final

address digit is dependent on pin CSBIWL, which should be tied to either DVDD or DGND. This

allows the device to have a choice of two identification header addresses used in the 2 wire

interface word. This feature allows more than one WM8728 device to be present on the interface

bus.

LATI2S should be tied to either DVDD or DGND, as it is unused. This pin if toggled from low to

high and high to low, will cause the device to enter the 3-wire interface mode and cannot be

placed back into 2-wire mode except by toggling the MODE pin, or powering off the device.

Figure 18 2-Wire Serial Interface