Production Data
WM8321
12.3 4-WIRE (SPI) CONTROL MODE
In this mode, the WM8321 registers are accessed using a 4-wire serial control interface. The C¯¯S and
SCLK1 pins provide the ‘Chip Select’ and ‘Serial Data Clock’ functions respectively. Serial data input
is supported on the SDA1 pin; serial data output is supported on the SDOUT1 pin.
A control word consists of 32 bits. The first bit is the read/write bit (R/W), which is followed by 15
address bits (A14 to A0) that determine which control register is accessed. The remaining 16 bits
(B15 to B0) are data bits, corresponding to the 16 bits in each control register.
In Write operations (R/W=0), all SDA1 bits are driven by the controlling device. Each rising edge of
SCLK1 clocks in one data bit from the SDA1 pin. A rising edge on C¯¯S latches in a complete control
word consisting of the last 32 bits.
In Read operations, the SDA1 pin is ignored following receipt of the valid register address. The data
bits are output by the WM8321 on the SDOUT1 pin. SDOUT1 is undriven (high impedance) when not
outputting register data bits.
The SDOUT1 pin is an Open Drain output; an external pull-up resistor to DBVDD is required on
SDOUT1 in 4-wire (SPI) mode.
The sequence of signals associated with a register write operation is illustrated in Figure 14.
CS
SCLK
SDIN
A14
A13
A12
A2
A1
A0
B15
B14
B13
B2
B1
B0
R/W
15-bit control register address
16-bit control register data
Figure 14 Control Interface 4-wire (SPI) Register Write
The sequence of signals associated with a register read operation is illustrated in Figure 15.
Figure 15 Control Interface 4-wire (SPI) Register Read
12.4 REGISTER LOCKING
Selected registers are protected by a security key. These registers can only be written to when the
appropriate ‘unlock’ code has been written to the Security Key register.
The protected registers include those associated with Reset Control, OTP Programming and RTC
Trim. Other selected functions also include protected registers; the affected registers are identified in
the Register Map definitions throughout the document, and also in Section 29.
To unlock the protected registers, a value of 9716h must be written to the Security register (R16392),
as defined in Table 13.
PD, February 2012, Rev 4.0
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