Si5345-44-42-D-RM
52
Rev. 1.0
9. Serial interface
Configuration and operation of the Si5345/44/42 is controlled by reading and writing registers using the I
2
C or SPI
interface. Both of these serial interfaces are based on 8-bit addressing, which means that the page byte must be
written every time you need to access a different page in the register map. See the PAGE byte at register 0x0001
for more information. The I2C_SEL pin selects I
2
C or SPI operation. The Si5345/44/42 supports communication
with a 3.3 or 1.8 V host by setting the IO_VDD_SEL (0x0943[0]) configuration bit. The SPI mode supports 4-wire or
3-wire by setting the SPI_3WIRE configuration bit.
Figure 23. I
2
C/SPI Device Connectivity Configurations
Table 35 lists register settings of interest for the I
2
C/SPI.
If neither serial interface is used, leave pins I2C_SEL, A1/SDO, and A0/CS disconnected, and tie SDA/SDIO and
SCLK low.
Table 35. I
2
C/SPI Register Settings
Register Name
Hex
Address
[Bit Field]
Function
IO_VDD_SEL
0x0943[0]
The IO_VDD_SEL bit determines whether the VDD or VDDA supply voltage is
used for the serial port, control pins, and status pins voltage references. See
the register map description of this bit for additional details.
SPI_3WIRE
0x002B[3]
The SPI_3WIRE configuration bit selects the option of 4-wire or 3-wire SPI
communication. By default, the SPI_3WIRE configuration bit is set to the 4-wire
option. In this mode, the Si5345/44/42 will accept write commands from a 4-
wire or 3- wire SPI host allowing configuration of device registers. For full bidi-
rectional communication in 3-wire mode, the host must write the SPI_3WIRE
configuration bit to “1”.
VDDA
VDD
1.8V
3.3V
Host = 3.3V
Host = 1.8V
I
2
C
I2C_SEL pin = High
IO_VDD_SEL
= 0
IO_VDD_SEL
= 0
I2C_SEL pin = Low
SPI
HOST
1.8V
SDI
SDO
CS
CS
SDO
SDI
SCLK
SCLK
Si5345/44/42
I
2
C
HOST
1.8V
VDDA
SCLK
SDA
1.8V
VDD
1.8V
3.3V
SPI
HOST
1.8V
SDIO
SDIO
CS
CS
SCLK
SCLK
SPI_3WIRE
= 0
SPI 4-Wire
SPI 3-Wire
I2C_SEL pin = Low
SPI_3WIRE
= 1
IO_VDD_SEL
= 0
IO_VDD_SEL
= 1
IO_VDD_SEL
= 1
IO_VDD_SEL
= 1
SCLK
SDA
(Default)
(Default)
VDDA
VDD
1.8V
3.3V
(Default)
VDDA
VDD
1.8V
3.3V
SPI
HOST
3.3V
SDI
SDO
CS
CS
SDO
SDI
SCLK
SCLK
I
2
C
HOST
3.3V
VDDA
SCLK
SDA
3.3V
VDD
1.8V
3.3V
SPI
HOST
3.3V
SDIO
SDIO
CS
CS
SCLK
SCLK
SCLK
SDA
VDDA
VDD
1.8V
3.3V
Si5345/44/42
Si5345/44/42
Si5345/44/42
Si5345/44/42
Si5345/44/42