2-Wire Serial Control Mode; Resetting The Chip - Cirrus Logic WM8940 Manual

RESETTING THE CHIP

Rev 4.4
Figure 36 Alternative 3-Wire Serial Control Timing
A limited number of Readback addresses are provided to enable ALC operation to be monitored and
to establish the identity and revision of the device.
REGISTER BIT
ADDRESS
R0 15:0 CHIP_ID
Software Reset
R1 2:0 DEVICE_REVIS
Power ON
Management 1
Table 56 Readback Registers

2-WIRE SERIAL CONTROL MODE

The WM8940 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 device address (this is not the same as the 7-bit
address of each register in the WM8940).
The WM8940 operates as a slave device only. 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 WM8940, then the WM8940 responds by pulling SDIN low on the next clock pulse
(ACK). If the address is not recognised or the R/W bit is '1' when operating in write only mode, the
WM8940 returns to the idle condition and wait for a new start condition and valid address.
During a write, once the WM8940 has acknowledged a correct address, the controller sends the first
byte of control data (B23 to B16, i.e. the WM8940 8 bit register address). The WM8940 then
acknowledges the first data byte by pulling SDIN low for one clock pulse. The controller then sends
the second byte of control data (B15 to B8, i.e. the most significant 8 bits of register data), and the
WM8940 acknowledges again by pulling SDIN low for one clock pulse. The controller then sends the
third byte of control data (B7 to B0, i.e. the remaining 8 bits of register data), and the WM8940
acknowledges again by pulling SDIN low for one clock pulse.
Transfers are complete when there is a low to high transition on SDIN while SCLK is high. After a
complete sequence the WM8940 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 jumps to the idle condition.
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Figure 37 2-Wire Serial Control Interface
In 2-wire mode the WM8940 has a fixed device address, 0011010.
The WM8940 can be reset by performing a write of any value to the software reset register (address 0
hex). This will cause all register values to be reset to their default values. In addition to this there is a
LABEL DEFAULT
Readback the CHIP ID
Readback the DEVICE_REVISON
WM8940
DESCRIPTION
63