Production Data
WM8741
2-WIRE SERIAL CONTROL MODE
The WM8741 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 (this is not the same as the 7-bit address
of each register in the WM8741).
The WM8741 operates as a slave device on the 2-wire control bus. 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 and data will follow. All devices on the 2-wire bus respond to the start condition and
shift in the next eight bits on SDIN (7-bit address + Read/Write bit, MSB first). If the device address
received matches the address of the WM8741 and the R/W bit is ‘0’, indicating a write, then the
WM8741 responds by pulling SDIN low on the next clock pulse (ACK). If the address is not
recognised or the R/W bit is ‘1’, the WM8741 returns to the idle condition and wait for a new start
condition and valid address.
Once the WM8741 has acknowledged a correct address, the controller sends the first byte of control
data (B15 to B8, i.e. the WM8741 register address plus the first bit of register data). The WM8741
then acknowledges the first data byte by pulling SDIN low for one clock pulse. The controller then
sends the second byte of control data (B7 to B0, i.e. the remaining 8 bits of register data), and the
WM8741 acknowledges again by pulling SDIN low.
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 WM8741 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 reverts to the idle condition.
Figure 13 2-wire Serial Control Interface
The WM8741 device address can be configured between two options. This is selected by the
SADDR pin.
PIN
NAME
DESCRIPTION
28
CSB/
0 = 2-wire address 0011010
SADDR/I2S 1 = 2-wire address 0011011
Table 10 2-wire Serial Control Mode Address Selection
DIGITAL AUDIO INTERFACE
PCM MODE
There are a number of valid PCM data input modes. Two channel and one channel differential mono
modes can be selected by serial or hardware control. It is also possible to bypass the WM8741
digital filters and apply a signal at a rate 8fs (where fs is the sampling rate) directly to the switched
capacitor stage..
PD, Rev 4.2, October 2009
21
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
