WM8978 Wolfson Microelectronics Ltd., WM8978 Datasheet - Page 77

• Manufacturer Part Number: WM8978
• Description: The WM8978 is a low power, high quality stereo codec designed for portable applications such as Digital still camera or Digital Camcorde
• Manufacturer: Wolfson Microelectronics Ltd.

Preliminary Technical Data
CONTROL INTERFACE
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SELECTION OF CONTROL MODE AND 2-WIRE MODE ADDRESS
Table 59 Control Interface Mode Selection
3-WIRE SERIAL CONTROL MODE
Figure 41 3-Wire Serial Control Interface
2-WIRE SERIAL CONTROL MODE
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 59.
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.
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.
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.
MODE
High
Low
INTERFACE FORMAT
2 wire
3 wire
PTD Rev 2.6 November 2005
WM8978
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