SAM3X8C Atmel Corporation, SAM3X8C Datasheet - Page 536

• Manufacturer Part Number: SAM3X8C
• Manufacturer: Atmel Corporation

28.1.5
28.1.5.1
536
536
SAM3X/A
SAM3X/A
Main Clock
4/8/12 MHz Fast RC Oscillator
Figure 28-3
Figure 28-3. Main Clock Block Diagram
The Main Clock has two sources:
After reset, the 4/8/12 MHz Fast RC Oscillator is enabled with the 4 MHz frequency selected and
it is selected as the source of MAINCK. MAINCK is the default clock selected to start up the
system.
The Fast RC Oscillator 8 and 12 MHz frequencies are calibrated in production. Note that is not
the case for the 4 MHz frequency.
Please refer to the “DC Characteristics” section of the product datasheet.
The software can disable or enable the 4/8/12 MHz Fast RC Oscillator with the MOSCRCEN bit
in the Clock Generator Main Oscillator Register (CKGR_MOR).
The user can also select the output frequency of the Fast RC Oscillator, either 4 MHz, 8 MHz or
12 MHz are available. It can be done through MOSCRCF bits in CKGR_MOR. When changing
• 4/8/12 MHz Fast RC Oscillator which starts very quickly and is used at startup.
• 3 to 20 MHz Crystal or Ceramic Resonator-based Oscillator which can be bypassed.
Slow Clock
shows the Main Clock block diagram.
XOUT
SLCK
XIN
Main Clock
MAINCK
Ref.
MOSCRCEN
MOSCRCEN
Ceramic Resonator
MOSCXTCNT
Main Clock
MOSCXTEN
MOSCXTEN
4/8/12 MHz
Frequency
Oscilla tor
3-20 MH z
Oscilla tor
3-20 MH z
Oscilla tor
Counter
Counter
Fast RC
Crystal
or
MOSCRCF
MOSCSEL
MAINRDY
MOSCRCS
MOSCXTS
MOSCSEL
MAINF
0
1
Main Clock
MOSCSELS
MAINCK
11057A–ATARM–17-Feb-12
11057A–ATARM–17-Feb-12