wm8987 Wolfson Microelectronics plc, wm8987 Datasheet - Page 43

• Manufacturer Part Number: wm8987
• Description: Stereo Codec For Portable Audio Applications
• Manufacturer: Wolfson Microelectronics plc

Production Data
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CONTROL INTERFACE
SELECTION OF CONTROL MODE
The WM8987L 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 data bits, corresponding to the 9 bits in each control
register. The control interface can operate as either a 3-wire or 2-wire MPU interface. The MODE pin
selects the interface format.
Table 39 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 latches in a complete control word consisting of the last 16 bits.
Figure 20 3-Wire Serial Control Interface
2-WIRE SERIAL CONTROL MODE
The WM8987L 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 WM8987L).
The WM8987L 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 WM8987L and the R/W bit is ‘0’, indicating a write, then the WM8987L 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 WM8987L returns to the idle condition and wait for a new start condition and valid address.
Once the WM8987L has acknowledged a correct address, the controller sends the first byte of
control data (B15 to B8, i.e. the WM8987L register address plus the first bit of register data). The
WM8987L 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 WM8987L 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 WM8987L 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.
Figure 21 2-Wire Serial Control Interface
SCLK
SCLK
SDIN
SDIN
CSB
MODE
High
START
Low
B15
B14
DEVICE ADDRESS
control register address
(7 BITS)
B13
B12
INTERFACE FORMAT
RD / WR
B11
BIT
2 wire
3 wire
B10
(LOW)
ACK
B9
register address and
CONTROL BYTE 1
1st register data bit
(BITS 15 TO 8)
B8
B7
B6
(LOW)
control register data bits
ACK
B5
CONTROL BYTE 2
B4
remaining 8 bits of
(BITS 7 TO 0)
register data
B3
PD Rev 4.0 August 2008
B2
(LOW)
ACK
B1
WM8987L
B0
latch
STOP
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