Cirrus Logic CS4391 - Manual (Page 33)

CS4391
DS335PP4 33
8. CONTROL PORT INTERFACE
The control port is used to load all the internal set-
tings of the CS4391. The operation of the control
port may be completely asynchronous to the audio
sample rate. However, to avoid potential interfer-
ence problems, the control port pins should remain
static if no operation is required.
The control port has 2 modes: SPI and I
2
C, with the
CS4391 operating as a slave device in both modes.
If I
2
C operation is desired, AD0/CS should be tied
to VA or AGND. If the CS4391 ever detects a high
to low transition on AD0/CS after power-up, SPI
mode will be selected. The control port registers
are write-only in SPI mode.
8.1 SPI Mode
In SPI mode, CS is the CS4391 chip select signal,
CCLK is the control port bit clock, CDIN is the in-
put data line from the microcontroller and the chip
address is 0010000. All signals are inputs and data
is clocked in on the rising edge of CCLK.
Figure 16 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 in-
dicator (R/W), which must 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. See Table 16.
The CS4391 has MAP auto increment capability,
enabled by the INCR bit in the MAP register. If
INCR is 0, then the MAP will stay constant for suc-
cessive writes. If INCR is set to 1, then MAP will
auto increment after each byte is written, allowing
block reads or writes of successive registers.
8.2 I
2
C Mode
In I
2
C mode, SDA is a bi-directional data line. Data
is clocked into and out of the part by the clock,
SCL, with the clock to data relationship as shown
in Figure 3. There is no CS pin. Pin AD0 forms the
partial chip address and should be tied to VA or
AGND as required. The upper 6 bits of the 7-bit ad-
dress field must be 001000. To communicate with
the CS4391 the LSB of the chip address field,
which is the first byte sent to the CS4391, should
match the setting of the AD0 pin. The eighth bit of
the address byte is the R/W bit (high for a read, low
for a write). If the operation is a write, the next byte
is the Memory Address Pointer, MAP, which se-
lects the register to be read or written. The MAP is
then followed by the data to be written. If the op-
eration is a read, then the contents of the register
pointed to by the MAP will be output after the chip
address.
The CS4391 has MAP auto increment capability,
enabled by the INCR bit in the MAP register. If
INCR is 0, then the MAP will stay constant for suc-
cessive writes. If INCR is set to 1, then MAP will
auto increment after each byte is written, allowing
block reads or writes of successive registers.
For more information on I
2
C, please see “The I2C-
Bus Specification: Version 2.0”, listed in the Ref-
erences section.