SAM4L Datasheet, PDF (158/1185 Pages) ATMEL Corporation – ATSAM ARM-based Flash MCU

ATSAM4L4/L2
If the reference clock stops when the RC32K is in closed loop mode, the RC32K Reference
Error bit (PCLKSR.RC32KREFE) is set, and the RC32K stays in closed loop mode, keeping the
current FINE value. When the reference clock starts again, the RC32K automatically resumes
the tracking of the reference clock.
In closed loop mode, if the correct frequency is out of range for the FINE value, it will saturate
due to an incorrect COARSE setting. The RC32K Saturation bit (PCLKSR.RC32KSAT) is set
and the user can read the current FINE value to determine further action. Note that
RC32KTUNE can only be written to when closed loop mode is disabled. When disabling closed
loop mode, wait for the RC32K Ready bit (PCLKSR.RC32KRDY) to be set before writing to
RC32KTUNE, and then wait for it to be set again before going back to closed loop mode. The
FINE field will always read as zeroes when in closed loop mode.
If the range of FINE is not sufficient to obtain the correct frequency, RC32KTUNE can be modi-
fied by the user with a new COARSE value to change the FINE offset. The user should select a
FINE value of 0x20 before enabling closed loop mode.
When the RC32K is enabled with either EN, EN32K, or EN1K in the RC32KCR register, the
oscillator is kept running during all Power Save Modes.
12.6.3
Brow-Out Detector (BOD) Operation
Rev: 1.1.0.0
The Brown-out Detectors BOD18 and BOD 33 monitors the VDDCORE and VDDIO supplies
respectively, and compares the voltage with the brown-out trigger level, as set in the
BOD18/33LEVEL register. The BOD is disabled by default, but can be enabled either by soft-
ware or by flash fuses. The Brown-out Detector can generate either an interrupt or a reset when
the supply voltage is below the Brown-out trigger level, as shown in Figure 12-2. The BOD18/33
detection status can be read from the Power and Clock Status Register
(PCLKSR.BOD18/33DET).
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