6. Serial Interface
Configuration and operation of the Si5386 is controlled by reading and writing registers using the I
2
C or SPI interface. The I
2
C_SEL pin
selects I
2
C or SPI operation. The Si5386 supports communication with a 3.3 V or 1.8 V host by setting the IO_VDD_SEL (0x0943[0])
configuration bit. The SPI interface supports both 4-wire or 3-wire modes by setting the SPI_3WIRE (0x002B[3]) configuration bit. See
the figure below for supported modes of operation and settings. All digital I/O pins are 3.3 V-tolerant, even when operating at 1.8 V.
Additionally, the pins with internal pull-ups, I2C_SEL and A0/CS are pulled-up to 3.3 V through a high impedance pull-up, regardless of
IO_VDD_SEL setting.
Host = 3.3V
Host = 1.8V
I
2
C
Serial
Interface
Configuration
I2C_SEL pin = High
IO_VDD_SEL
= 0
IO_VDD_SEL
= 0
I2C_SEL pin = Low
Clock IC
SPI
HOST
1.8V
VDDA
VDD
SDIO
SDO
CSb
CSb
SDO
SDI
SCLK
SCLK
1.8V
3.3V
Clock IC
I
2
C
HOST
1.8V
VDDA
SCLK
SDA
1.8V
VDD
1.8V
3.3V
Clock IC
SPI
HOST
1.8V
VDDA
VDD
SDIO
SDIO
CSb
CSb
SCLK
SCLK
1.8V
3.3V
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
Clock IC
SPI
HOST
3.3V
VDDA
VDD
SDO
CSb
SDI
SCLK
1.8V
3.3V
Clock IC
I
2
C
HOST
3.3V
VDDA
SCLK
SDA
SCLK
SDA
3.3V
VDD
1.8V
3.3V
Clock IC
SPI
HOST
3.3V
VDDA
VDD
SDIO
SDIO
CSb
CSb
SCLK
SCLK
1.8V
3.3V
IO_VDD_SEL
= 1
SCLK
SDA
SDIO
CSb
SDO
SCLK
Figure 6.1. I2C/SPI Device Connectivity Configurations
In some cases it is not known prior to the design, what the serial interface type and I/O voltage will be. Setting the device to 1.8 V
(IO_VDD_SEL = 0) digital I/O in the NVM allows the host to reliably write the device, regardless of its operating voltage. Once the serial
interface type has been chosen using the I
2
C_SEL pin, the device may be written successfully regardless of the host interface type.
This is true for both 3-wire and 4-wire SPI modes as well as I
2
C. The SPI serial data is written to the same SDA/SDIO input pin in
all cases. At this point, the device can be configured to adjust IO_VDD_SEL for optimum 3.3 V operation and to select SPI_3WIRE
between 3-/4-wire SPI modes. These mode changes are made immediately and no delays or wait times are needed for subsequent
serial interface operations, including read operations.
Note that the registers are organized into multiple pages to allow a larger register set, given the limitations of the I
2
C/SPI interface
standards. First, the correct page must be selected with the initial write. Then the register location within that page can be read/written.
See "
AN926: Reading and Writing Registers with SPI and I
" for more information on register paging.
If neither serial interface is used, the SDA/SDIO, A1/SDO, and SCLK pins must be pulled either high or low externally since they are not
pulled internally. I
2
C_SEL and A0/CSb have internal pull-ups and may be left unconnected in this case. Note that the Si5386 is not I
2
C
failsafe upon loss of power. Applications that require failsafe operation should isolate the device from a shared I
2
C bus.
Si5386 Rev. E Reference Manual • Serial Interface
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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Rev. 1.2 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • December 9, 2021
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