WM8950 datasheet(45/60 Pages) CIRRUS

45 / 60 page

WM8950

Rev 4.5

2-WIRE SERIAL CONTROL MODE

The WM8950 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 WM8950).

The WM8950 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 WM8950, then the WM8950 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

WM8950 returns to the idle condition and wait for a new start condition and valid address.

During a write, once the WM8950 has acknowledged a correct address, the controller sends the first

byte of control data (B15 to B8, i.e. the WM8950 register address plus the first bit of register data).

The WM8950 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 WM8950 acknowledges again by pulling SDIN low.

Transfers are complete when there is a low to high transition on SDIN while SCLK is high. After a

complete sequence the WM8950 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.

SDIN

SCLK

1st register data bit

DEVICE ADDRESS

(7 BITS)

RD / WR

BIT

ACK

(LOW)

CONTROL BYTE 1

(BITS 15 TO 8)

CONTROL BYTE 1

(BITS 7 TO 0)

remaining 8 bits of

STOP

START

ACK

(LOW)

ACK

(LOW)

Figure 28 2-Wire Serial Control Interface

In 2-wire mode the WM8950 has a fixed device address, 0011010.

RESETTING THE CHIP

The WM8950 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 Power-On Reset (POR) circuit which ensures that the registers are set to default when the device

is powered up.

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