WM8778 datasheet(22/50 Pages) WOLFSON

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WM8778

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PP Rev 1.7 June 2004

B[15:9] are Control Address Bits

B[8:0] are Control Data Bits

CE is edge sensitive – the data is latched on the rising edge of CE.

2-WIRE SERIAL CONTROL MODE

The WM8778 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 WM8778).

The WM8778 operates as a slave device only. The controller indicates the start of data transfer with

a high to low transition on DI while CL 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 DI (7-bit address + Read/Write bit, MSB first). If the device address received matches the address

of the WM8778 and the R/W bit is ‘0’, indicating a write, then the WM8778 responds by pulling DI low

on the next clock pulse (ACK). If the address is not recognised or the R/W bit is ‘1’, the WM8778

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

Once the WM8778 has acknowledged a correct address, the controller sends the first byte of control

data (B15 to B8, i.e. the WM8778 register address plus the first bit of register data). The WM8778

then acknowledges the first data byte by pulling DI 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 WM8778

acknowledges again by pulling DI low.

The transfer of data is complete when there is a low to high transition on DI while CL is high. After

receiving a complete address and data sequence the WM8778 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. DI changes while CL is high), the device jumps to the idle condition.

Figure 20 2-wire Serial Interface

B[15:9] are Control Address Bits

B[8:0] are Control Data Bits

The WM8778 has two possible device addresses, which can be selected using the CE pin.

CE STATE

DEVICE ADDRESS

Low

0011010 (0 x 34h)

High

0011011 (0 x 36h)

Table 11 2-Wire MPU Interface Address Selection

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