STMicroelectronics SPEAr300, Reference Manual

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BS_System controller RM0082
290/844 Doc ID 018672 Rev 1
14.3.2 System control state machine
Figure 24. System mode control state machine
Crystal oscillator and PLL control
The system control state machine ( Section 14.3.2: System control state machine ) can also
be used to control the crystal oscillator and the PLL.
Nevertheless, software can be used to override control of the crystal and PLL by using the
crystal control register (SCXTALCTRL,
Section 14.4.7 ) and the PLL control register
(SCPLLCTRL).
PLL frequency control
To define the frequency of the clock generated from the PLL, the system controller provides
a PLL frequency control register (SCPLLFCTRL,
Section 14.3.5 ).
PLLSW
NORMAL
SW From
PLL
NORMAL
PLL SW
NORMAL
PLLON ||(PLLTIMEEN && PLL Timeout)
SW to
PLL
SLOW
SW From
XTAL
DOZE
XTAL
CTL
SW to
XTAL
SLOW&NORMAL
XTALSW
SLOW |
NORMAL
XTALON ||(XTALTIMEEN && XTAL Timeout)
XTAL SW
IRQ | FIQ
DOZE&SLOW&NORMAL
&STANDBYWFI
nPOR
SLEEP
PLL
CTL