WM8956GEFLSLASHV datasheet(57/80 Pages) WOLFSON

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Preliminary Technical Data

WM8956

PTD, July 2007, Rev 2.1

CONTROL INTERFACE

2-WIRE SERIAL CONTROL INTERFACE

The WM8956 is controlled by writing to registers through a 2-wire serial control interface. A control

word consists of 16 bits. The first 7 bits (B15 to B9) are address bits that select which control register

is accessed. The remaining 9 bits (B8 to B0) are data bits, corresponding to the 9 bits in each control

address (this is not the same as the 7-bit address of each register in the WM8956).

The device address is 0011010 (0x34h).

The WM8956 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 WM8956 and the R/W bit is ‘0’, indicating a write, then the WM8956 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 WM8956 returns to the idle condition and wait for a new start condition and valid address.

Once the WM8956 has acknowledged a correct address, the controller sends the first byte of control

data (B15 to B8, i.e. the WM8956 register address plus the first bit of register data). The WM8956

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

WM8956 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 WM8956 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 2

(BITS 7 TO 0)

remaining 8 bits of

STOP

START

ACK

(LOW)

ACK

(LOW)

Figure 35 2-Wire Serial Control Interface

POWER MANAGEMENT

The WM8956 has three control registers that allow users to select which functions are active. For

minimum power consumption, unused functions should be disabled. To avoid any pop or click noise,

it is important to enable or disable functions in the correct order (see Applications Information).

VMIDSEL is the enable for the Vmid reference, which defaults to disabled and can be enabled as a

2x50k

Ω potential divider or, for low power maintenance of Vref when all other blocks are disabled, as

a 2x250k

Ω potential divider.

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