CS8405 datasheet(14/36 Pages) CIRRUS

14 / 36 page

CS8405A

DS469PP4

6. CONTROL PORT DESCRIPTION

AND TIMING

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

lowing the CS8405A to be configured for the de-

sired operational modes and formats. In addition,

Channel Status and User data may be read and writ-

ten through the control port. The operation of the

control port may be completely asynchronous with

respect to the audio sample rate.

The control port has two modes: SPI and Two-

Wire, with the CS8405A acting as a slave device.

SPI mode is selected if there is a high to low tran-

sition on the AD0/CS pin after the RST pin has

been brought high. Two-Wire mode is selected by

connecting the AD0/CS pin to VL+ or DGND,

thereby permanently selecting the desired AD0 bit

address state.

6.1

SPI Mode

In SPI mode, CS is the CS8405A chip select signal,

CCLK is the control port bit clock (input into the

CS8405A from the microcontroller); CDIN is the

input data line from the microcontroller; and CD-

OUT 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 8 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 0010000. The eighth bit is a read/write in-

dicator (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, then the MAP

will auto increment after each byte is read or writ-

ten, allowing block reads or writes of successive

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

MA P

MSB

LSB

DATA

byte 1

by te n

R/W

AD D R ESS

CH IP

ADDRESS

CHI P

CD IN

CCL K

CD OU T

MSB

LSB MSB

LSB

0010000

MAP = Memory Address Pointer, 8 bits, MSB first

High Impedance

Figure 8. Control Port Timing in SPI Mode

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