CS8420 datasheet(26/80 Pages) CIRRUS

26 / 80 page

CS8420

DS245PP2

10. CONTROL PORT DESCRIPTION

AND TIMING

The control port is used to access the registers, al-

lowing the CS8420 to be configured for the desired

operational modes and formats. In addition, Chan-

nel Status and User data may be read and written

via the control port. The operation of the control

port may be completely asynchronous with respect

to the audio sample rates. However, to avoid poten-

tial 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

CS8420 acting as a slave device. SPI mode is se-

lected 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 to VD+ or DGND, thereby perma-

nently selecting the desired AD0 bit address state.

10.1

SPI Mode

In SPI mode, CS is the CS8420 chip select signal,

CCLK is the control port bit clock (input into the

CS8420 from the microcontroller), CDIN is the in-

put 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 24 shows the operation of the control port in

SPI mode. To write to a register, bring CS low. The

first 7 bits on CDIN form the chip address and must

be 0010000. The eighth bit is a read/write indicator

(R/W), which should be low to write. The next 8

bits form the Memory Address Pointer (MAP),

which is set to the address of the register that is to

be updated. The next 8 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, then the MAP will stay constant for succes-

sive read or writes. If INCR is set to a 1, then the

MAP will auto-increment after each byte is read or

written, allowing block reads or writes of succes-

sive registers.

To read a register, the MAP has to be set to the cor-

rect address by executing a partial write cycle

which finishes (CS high) immediately after the

MAP byte. The MAP auto increment bit (INCR)

MA P

MSB

LSB

DATA

by te 1

by te n

R/W

AD D R ES S

CH IP

ADDRESS

CH IP

CD IN

CC L K

CD O U T

MSB

LSB MSB

LSB

0010000

MAP = Memory Address Pointer, 8 bits, MSB first

High Impedance

Figure 24. Control Port Timing in SPI Mode

CS8420 Datasheet(PDF) 26 Page - Cirrus Logic

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