WM8805 datasheet(16/66 Pages) CIRRUS

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WM8805

Production Data

PD, Rev 4.5, March 2009

Figure 10 3-Wire Control Interface Read-Back Method 2

2-WIRE SERIAL CONTROL WITH READ-BACK MODE

The WM8805 supports software control via a 2-wire serial bus. Many devices can be controlled by

the same bus and each device has a unique 7-bit address (see Table 11).

The controller indicates the start of data transfer with a high to low transition on SDIN while SCLK

remains high. This indicates that a device address, DEVA(7:1), and data, REG(6:0), will follow. All

devices on the 2-wire bus will shift in the next eight bits on SDIN (7-bit address DEVA(7:1), +

read/write ‘W’ bit, MSB first). If the device address received matches the address of the WM8805,

the WM8805 responds by driving SDIN low on the next clock pulse (ACK). This is a device

acknowledgement of an address match. If the address does not match that of the WM8805, the

device returns to the idle condition and waits for a new start condition and valid address.

Once the WM8805 has acknowledged a matching address, the controller sends the first byte of

control data, which is the WM8805 register address (REGA[6:0]). The WM8805 then acknowledges

reception of the control data byte by pulling SDIN low for one clock pulse (another ACK). The

controller then sends the second byte of control data (DIN[7:0], i.e. the eight bits of register data to

be written), and the WM8805 acknowledges again by pulling SDIN low (another ACK).

The transfer of data is complete when there is a low to high transition on SDIN while SCLK is high.

After receiving a complete address and data sequence the WM8805 returns to the idle state and

waits for another start condition. If a start or stop condition is detected out of sequence at any point

during data transfer (i.e. SDIN changes while SCLK is high), the device returns to the idle condition.

Figure 11 2-Wire Serial Control Interface Write

Multiple consecutive register writes can be performed in 2-wire control mode by setting the CONT bit

high. This method allows the entire register map to be defined in a one continuous write operation.

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