Atmel ARM-Based Evaluation Kit for SAM4S16C, 32-Bit ARM® Cortex® Microcontroller ATSAM4S-WPIR-RD ATSAM4S-WPIR-RD Data Sheet
Product codes
ATSAM4S-WPIR-RD
501
SAM4S Series [DATASHEET]
Atmel-11100G-ATARM-SAM4S-Datasheet_27-May-14
28.5
Main Clock
shows the main clock block diagram.
Figure 28-3.
Main Clock Block Diagram
The main clock has two sources:
4/8/12 MHz fast RC oscillator which starts very quickly and is used at start-up.
3 to 20 MHz crystal or ceramic resonator-based oscillator which can be bypassed.
28.5.1 Fast RC Oscillator
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 frequencies are calibrated in production except the lowest frequency which is not calibrated.
Refer to the “DC Characteristics” section of the product datasheet.
The fast RC oscillator frequencies are calibrated in production except the lowest frequency which is not calibrated.
Refer to the “DC Characteristics” section of the product datasheet.
XIN
XOUT
MOSCXTEN
MOSCXTST
MOSCXTS
Main Clock
Frequency
Counter
MAINF
SLCK
Slow Clock
3-20 MHz
Crystal
or
Ceramic Resonator
Oscillator
3-20 MHz
Oscillator
Counter
MOSCRCEN
Fast RC
Oscillator
MOSCRCS
MOSCRCF
MOSCRCEN
MOSCXTEN
MOSCSEL
MOSCSEL
MOSCSELS
1
0
MAINCK
Main Clock
Main Clock
MAINCK
Main Clock
Ref.
RCMEAS
CKGR_MCFR
CKGR_MOR
CKGR_MOR
CKGR_MOR
PMC_SR
PMC_SR
CKGR_MOR
CKGR_MOR
CKGR_MOR
CKGR_MOR
CKGR_MOR
CKGR_MCFR
PMC_SR
CKGR_MCFR
MAINFRDY