Atmel Xplained Pro Evaluation Kit ATSAM4E-XPRO ATSAM4E-XPRO データシート

SAM4E [DATASHEET]

Atmel-11157D-ATARM-SAM4E16-SAM4E8-Datasheet_12-Jun-14

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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 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 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 4/8/12 MHz are available. It can be
done through MOSCRCF bits in CKGR_MOR. When changing this frequency selection, the MOSCRCS bit in the
Power Management Controller Status Register (PMC_SR) is automatically cleared and MAINCK is stopped until
the oscillator is stabilized. Once the oscillator is stabilized, MAINCK restarts and MOSCRCS is set.

When disabling the main clock by clearing the MOSCRCEN bit in CKGR_MOR, the MOSCRCS bit in PMC_SR is
automatically cleared, indicating the main clock is off.

Setting the MOSCRCS bit in the Power Management Controller Interrupt Enable Register (PMC_IER) can trigger
an interrupt to the processor.

When main clock (MAINCK) is not used to drive the processor and frequency monitor (SLCKis used instead), it is
recommended to disable the main oscillators.

The CAL4, CAL8 and CAL12 values in the PMC Oscillator Calibration Register (PMC_OCR) are the default values
set by Atmel during production. These values are stored in a specific Flash memory area different from the main
memory plane. These values cannot be modified by the user and cannot be erased by a Flash erase command or
by the ERASE pin. Values written by the user's application in PMC_OCR are reset after each power up or
peripheral reset.