RM0082
BS_System controller
Doc ID 018672 Rev 1
289/844
XTAL control transition state, XTAL CTL
XTAL control transition state is used to initialize the crystal oscillator. While in this state, both
the system clocks and the System Controller clock are driven from a low-frequency
oscillator.
The system moves into the Switch to XTAL transition state when the crystal oscillator output
is stable. This is indicated when either the XTAL timeout defined in the XTAL control register
expires (when the XTALTIMEEN input is valid) or by the XTALON input being set to logic ‘1’.
Switch to XTAL transition state, SW TO XTAL
Switch to XTAL transition state is used to initiate the switching of the system clock source
from the slow speed oscillator to the crystal oscillator. The system moves into the SLOW
mode when the XTALSW input is set to logic ‘1’, to indicate that the clock switching is
complete.
Switch from XTAL transition state (SW from XTAL)
The “Switch from XTAL” transition state is entered when moving from SLOW to DOZE mode.
It is used to initiate the switching of the system clock source from the crystal oscillator to the
low speed oscillator. The system moves into the DOZE mode when the XTALSW input is set
to PLL control transition state (PLL CTL)
The “PLL control” transition state is used to initialize the PLL. While in this state, both the
system clocks and the System Controller clock are driven by the output of the crystal
oscillator.
The system moves then into the “Switch to PLL” transition state when the PLL timeout
defined in the PLL control register (SCPLLCTRL register) expires (when the PLLTIMEEN
input is invalid) and if the PLLON input is set to logic1.
Switch to PLL transition state (SW to PLL)
The “Switch to PLL” transition state is used to initiate the switching of the system clock
source from the crystal oscillator to the PLL output.
The system moves then into the NORMAL mode when the PLLSW input is set to logic ‘1’ to
indicate that the clock switching is complete.
Switch from PLL transition state (SW from PLL)
The “Switch from PLL” transition state is entered when moving from NORMAL to SLOW
mode. It is used to initiate the switching of the clock sources from the PLL to the crystal
oscillator output.
The system moves then into the SLOW mode when the PLLSW input is set to logic ‘0’ to
indicate that the clock switching is complete.