WM8978CGEFLSLASHV datasheet(82/118 Pages) WOLFSON

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WM8978

Production Data

PD, Rev 4.5, October 2011

CONTROL INTERFACE

SELECTION OF CONTROL MODE AND 2-WIRE MODE ADDRESS

The control interface can operate as either a 3-wire or 2-wire MPU interface. The MODE pin

determines the 2 or 3 wire mode as shown in Table 63.

The WM8978 is controlled by writing to registers through a 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 register bits, corresponding to the 9 bits in each

control register.

MODE

INTERFACE FORMAT

Low

2 wire

High

3 wire

Table 63 Control Interface Mode Selection

3-WIRE SERIAL CONTROL MODE

In 3-wire mode, every rising edge of SCLK clocks in one data bit from the SDIN pin. A rising edge on

CSB/GPIO1 pin latches in a complete control word consisting of the last 16 bits.

Figure 44 3-Wire Serial Control Interface

2-WIRE SERIAL CONTROL MODE

The WM8978 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 WM8978).

The WM8978 operates as a slave 2-wire 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 WM8978, then the WM8978 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 WM8978 returns to the idle condition and wait for a new start condition and valid address.

During a write, once the WM8978 has acknowledged a correct address, the controller sends the first

byte of control data (B15 to B8, i.e. the WM8978 register address plus the first bit of register data).

The WM8978 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 WM8978 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 WM8978 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 45 2-Wire Serial Control Interface

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