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The Voltage Regulator OK bit (VREGCR.VREGOK) bit indicates when the voltage regulator out-
put has reached the voltage threshold level.
13.5.7.3
Factory calibration
After a Power-on Reset (POR) the VREGCR.CALIB field is loaded with a factory defined calibra-
tion value. This value is chosen so that the normal output voltage of the regulator after a power-
up is 1.8V.
Although it is not recommended to override default factory settings, it is still possible to override
these default values by writing to VREGCR.CALIB.
If the Flash Calibration Done bit in VREGCR (VREGCR.FCD) is zero, the flash calibration will be
redone after any reset, and the VREGCR.FCD bit will be set before program execution starts in
the CPU. If VREGCR.FCD is one, the flash calibration will only be redone after a POR.
13.5.7.4
POR33 control
VREGCR includes control bits for the Power-on Reset 3.3V (POR33) detector that monitors the
internal regulator supply voltage. The POR33 detector is enabled by default but can be disabled
by software to reduce power consumption. The 3.3V Supply Monitor (SM33) can then be used to
monitor the regulator power supply.
T h e POR3 3 de tect or is d i sab l e d by writing a ze ro to th e POR3 3 Enab le bit
(VREGCR.POR33EN). Because of internal synchronisation, the POR33 detector is not immedi-
ately enabled or disabled. The actual state of the POR33 detector can be read from the POR33
Status bit (VREGCR.POR33STATUS).
The 32kHz RC oscillator (RC32K) must be enabled before disabling the POR33 detector. Once
the POR33 detector has been disabled, the RC32K oscillator can be disabled again.
To avoid spurious resets, it is mandatory to mask the Power-on Reset when enabling or dis-
abling the POR33 detector. The Power-on Reset generated by the POR33 detector can be
ignored by writing a one to the POR33 Mask bit (VREGCR.POR33MASK). Because of internal
synchronization, the masking is not immediately effective, so software should wait for the
VREGCR.POR33MASK to read as a one before assuming the masking is effective.
13.5.8
3.3 V Supply Monitor (SM33)
Rev: 1.0.0.0
The 3.3V supply monitor is a specific voltage detector for the internal regulator supply voltage. It
will indicate if the internal regulator supply voltage is above the minimum required input voltage
threshold. The user can choose to generate either a Power-on Reset (POR) and an interrupt
request, or only an interrupt request, when the internal regulator supply voltage drops below this
threshold.
Please refer to the Electrical Characteristics chapter for parametric details.
13.5.8.1
Register protection
To prevent unexpected writes to SM33 register due to software bugs, write access to this regis-
ter is protected by a locking mechanism. For details please refer to the UNLOCK register
description.