4. Power-up, Reset, and Initialization
Once power is applied, the device begins an initialization period where it downloads default register values and configuration data
from NVM and performs other initialization tasks. Communicating with the device through the serial interface is possible once this
initialization period is complete. No clocks will be generated until the initialization is complete.
Power-Up
Serial interface
ready
RST
pin asserted
Hard Reset
bit asserted
Initialization
NVM download
Soft Reset
bit asserted
Figure 4.1. Initialization from Power-up, Hard Reset, and Soft Reset
There are two types of commanded resets available.
1. The first is the hard reset. A hard reset is functionally similar to a device power-up. All registers will be restored to the values stored
in NVM, and all circuits will be restored to their initial state including the serial interface. A hard reset is initiated using the RST pin
or by asserting the hard reset register bit.
2. The second type of reset is a
soft
reset. Asserting the soft reset rgister bit
bypasses
the NVM download and simply re-starts the
internal initialization sequence.
NVM
2x
OTP
RAM
NVM Download
Figure 4.2. Si5391/Si5391P Memory Configuration
Table 4.1. Reset Control Registers
Register Name
Hex Address [Bit Field]
Function
Si5391
HARD_RST
001E[1]
Performs the same function as power cycling the device. All registers will be
restored to their default values.
SOFT_RST
001C[0]
Performs a soft reset. Resets the device while it does not re-download the
register configuration from NVM.
The Si5391/Si5391P is fully configurable using the serial interface (I
2
C or SPI). At power-up the device downloads its default register
values from internal non-volatile memory (NVM). Application specific default configurations can be pre-written into NVM allowing the
device to generate specific clock frequencies at power-up. Writing default values to NVM is in-circuit programmable with normal
operating power supply voltages applied to its VDD (1.8 V) and VDDA (3.3 V) pins. Neither VDDOx or VDDS supplies are required to
write the NVM.
Si5391 Reference Manual • Power-up, Reset, and Initialization
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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