CS42418 datasheet(26/67 Pages) CIRRUS

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CS42418

3.6

Control Port Description and Timing

The control port is used to access the registers, allowing the CS42418 to be configured for the desired op-

erational modes and formats. The operation of the control port may be completely asynchronous with re-

spect to the audio sample rates. However, to avoid potential interference problems, the control port pins

should remain static if no operation is required.

The control port has 2 modes: SPI and I2C, with the CS42418 acting as a slave device. SPI mode is selected

if there is a high to low transition on the AD0/CS pin, after the RST pin has been brought high. I2C mode

is selected by connecting the AD0/CS pin through a resistor to VLC or DGND, thereby permanently se-

lecting the desired AD0 bit address state.

3.6.1

SPI Mode

In SPI mode, CS is the CS42418 chip select signal, CCLK is the control port bit clock (input into the

CS42418 from the microcontroller), CDIN is the input data line from the microcontroller, CDOUT is the

output data line to the microcontroller. Data is clocked in on the rising edge of CCLK and out on the falling

edge.

Figure 17 shows the operation of the control port in SPI mode. To write to a register, bring CS low. The

first seven bits on CDIN form the chip address and must be 1001111. The eighth bit is a read/write indi-

cator (R/W), which should be low to write. The next eight bits form the Memory Address Pointer (MAP),

which is set to the address of the register that is to be updated. The next eight bits are the data which will

be placed into the register designated by the MAP. During writes, the CDOUT output stays in the Hi-Z

state. It may be externally pulled high or low with a 47 k

Ω resistor, if desired.

There is a MAP auto increment capability, enabled by the INCR bit in the MAP register. If INCR is a zero,

the MAP will stay constant for successive read or writes. If INCR is set to a 1, the MAP will autoincrement

after each byte is read or written, allowing block reads or writes of successive registers.

To read a register, the MAP has to be set to the correct address by executing a partial write cycle which

finishes (CS high) immediately after the MAP byte. The MAP auto increment bit (INCR) may be set or

MA P

MSB

LSB

DATA

byte 1

byte n

R/W

A DDRE S S

CH IP

ADDRESS

CHIP

CDIN

CCL K

CD O U T

MSB

LSB MSB

LSB

1001111

MAP = Memory Address Pointer, 8 bits, MSB first

High Impedance

Figure 17. Control Port Timing in SPI Mode

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