Cirrus Logic CS42428 - Manual (Page 35)

DS605F2 35
CS42428
4.6.1 SPI Mode
In SPI mode, CS is the CS42428 chip-select signal; CCLK is the control port bit clock (input into the
CS42428 from the microcontroller); CDIN is the input data line from the microcontroller, and 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 21 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
 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 auto-increment
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 not,
as desired. To begin a read, bring CS low, send out the chip address and set the read/write bit (R/W) high.
The next falling edge of CCLK will clock out the MSB of the addressed register (CDOUT will leave the high
SCLK_PORT1
LRCK_PORT1
SDIN_PORT1
SDIN_PORT2
SCLK_PORT2
LRCK_PORT2
SDOUT1_PORT2
SDOUT2_PORT2
SDOUT3_PORT2
SDOUT4_PORT2
RMCK
ADCIN1
ADCIN2
64Fs,128Fs, 256Fs
DIGITAL AUDIO
PROCESSOR
ADC_SCLK
ADC_LRCK
ADC_SDOUT
DAC_SCLK
DAC_LRCK
DAC_SDIN1
DAC_SDIN2
DAC_SDIN3
DAC_SDIN4
64Fs,128Fs
MCLK
Figure 20. OLM Configuration #4
CS42426
M A P
MSB LSB
DATA
b y te 1 b y te n
R/W R/W
A D D R E S S
C H IP
ADDRESS
C H IP
C D IN
C C L K
CS
C D O U T
MSB LSB MSB LSB
1001111 1001111
MAP = Memory Address Pointer, 8 bits, MSB first
High Impedance
Figure 21. Control Port Timing in SPI Mode