WM8785

Pre-Production

w

PP Rev 3.0 December 2005

22

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 latches in a complete control word consisting of the last 16 bits.

B15

B14

B13

B12

B11

B10

B9

B8

B7

B6

B5

B4

B3

B2

B1

B0

SDIN

SCLK

CSB

control register address

control register data bits

latch

Figure 26 3-Wire Serial Control Interface

2-WIRE SERIAL CONTROL MODE

The WM8785 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 WM8785).

The WM8785 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 WM8785 and the R/W bit is ‘0’, indicating a write, then the WM8785 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 WM8785 returns to the idle condition and wait for a new start condition and valid address.

Once the WM8785 has acknowledged a correct address, the controller sends the first byte of control

data (B15 to B8, i.e. the WM8785 register address plus the first bit of register data). The WM8785

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

WM8785 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 WM8785 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

register address and

1st register data bit

DEVICE ADDRESS

(7 BITS)

RD / WR

BIT

ACK

(LOW)

CONTROL BYTE 1

(BITS 15 TO 8)

CONTROL BYTE 1

(BITS 15 TO 8)

remaining 8 bits of

register data

STOP

START

ACK

(LOW)

ACK

(LOW)

Figure 27 2-Wire Serial Control Interface

The WM8785 device address is 0011010.

TIME DIVISION MULTIPLEXED DATA OUT

The WM8785 can be used to time division multiplex several data channels at once. For example, the

diagram below illustrates 4 devices connected to the same TDM bus. While one DOUT pin is driving

data, the others will be tri-stated.