Table 11.1. I
2
C/SPI Register Settings
Setting Name
Hex Address [Bit Field]
Function
Si5391/Si5391P
IO_VDD_SEL
0x0943[0]
The IO_VDD_SEL configuration bit optimizes the V
IL
, V
IH
, V
OL
,
and V
OH
thresholds to match the VDDS voltage. By default the
IO_VDD_SEL bit is set to the VDD option. The serial interface
pins are always 3.3 V tolerant even when the device's VDD pin
is supplied from a 1.8 V source. When the I
2
C or SPI host is
operating at 3.3 V and the Si5391/Si5391P at VDD = 1.8 V, the
host must write the IO_VDD_SEL configuration bit to the VDDA
option. This will ensure that both the host and the serial interface
are operating at the optimum voltage thresholds.
SPI_3WIRE
0x002B[3]
The SPI_3WIRE configuration bit selects the option of 4-wire or
3-wire SPI communication. By default, this configuration bit is set
to the 4-wire option. In this mode the Si5391/Si5391P will accept
write commands from a 4-wire or 3- wire SPI host allowing config-
uration of device registers. For full bidirectional communication in
3-wire mode, the host must write the SPI_3WIRE configuration bit
to “1”.
Si5391 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. 0.5 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • January 11, 2022
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