SAM3S8B Atmel Corporation, SAM3S8B Datasheet - Page 442

• Manufacturer Part Number: SAM3S8B
• Manufacturer: Atmel Corporation

25.0.5
25.0.5.1
442
442
SAM3S8/SD8
SAM3S8/SD8
Main Clock
4/8/12 MHz Fast RC Oscillator
Figure 25-3
Figure 25-3. 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.
Main Clock
Slow Clock
shows the Main Clock block diagram.
MAINCK
XOUT
SLCK
XIN
Ref.
MOSCRCEN
MOSCRCEN
Ceramic Resonator
MOSCXTCNT
MOSCXTEN
MOSCXTEN
4/8/12 MHz
Oscilla tor
3-20 MH z
Oscilla tor
3-20 MH z
Oscilla tor
Counter
Fast RC
Crystal
or
Main Clock
Frequency
Counter
MOSCRCF
MOSCSEL
RCMEAS
MOSCRCS
MOSCXTS
MOSCSEL
0
1
MAINRDY
MAINF
MOSCSELS
MAINCK
Main Clock
11090A–ATARM–10-Feb-12
11090A–ATARM–10-Feb-12