Atmel SAM9X25, Manual

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11054A–ATARM–27-Jul-11
SAM9X25
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11054A–ATARM–27-Jul-11
SAM9X25
Figure 21-4. Main Clock Selection
MOSCRCEN, MOSCXTEN, MOSCSEL and MOSCXTBY bits are located in the PMC Clock
Generator Main Oscillator Register (CKGR_MOR).
After a VDDBU power on reset, the default configuration is MOSCRCEN = 1, MOSCXTEN = 0
and MOSCSEL = 0, the 12 MHz RC oscillator is started as Main clock.
21.6.1 Fast wake-up
To speed up the wake-up phase, the system boots on 12 MHz RC (Main Clock). This allows the
user to perform system configuration (PLL, DDR2, etc.) at 12 MHz instead of 32 kHz during
12 MHz oscillator start-up.
Figure 21-5. PMC Startup
On Chip
12M RC OSC
Main Clock
Main Clock
Oscillator
MOSCXTEN
MOSCRCEN
MOSCSEL
XIN
XOUT
MOSCXTBY
Extern a l M a in Cock
M a in Su pply
POR o u tp u t
12 MHz RC S t a rt u p Time
W a it MO S CRC S = 1
S y s tem s witche s on M a in Clock
to s peed- u p the b oot
S y s tem i s r u nning a t 12 MHz
Extern a l o s cill a tor
i s s t a rted for b etter a cc u r a cy
MO S CXTEN = 1
MO S C S EL = 0
S y s tem s t a rt s on 3 2 kHz RC
RCEN = 1
O
S C 3 2EN = 0
O S C S EL = 0
MO S CRCEN = 1
MO S CXTEN = 0
MO S C S EL = 0
PMC_MCKR = 1
Cry s t a l S t a rt u p Time
W a it MO S CXT S = 1
U s er s witche s on extern a l o s cill a tor
MO S C S EL=1
W a it while MO S C S EL S =1
S y s tem i s r u nnning on 12 MHz Cry s t a l
PLL c a n b e us ed
12 MHz RC