SAM4L Datasheet, PDF (160/1185 Pages) ATMEL Corporation – ATSAM ARM-based Flash MCU

ATSAM4L4/L2
12.6.3.3
12.6.3.4
Continuous Mode
When BOD18/33CTRL.MODE is zero, the BOD18/33 operates in continuous mode. In continu-
ous mode the BOD18/33 is enabled and continously monitoring the supply voltage. The
continuos mode is the default mode.
Sampling Mode
The sampling mode, also called the one-shot mode, is a low power mode where the BOD18/33
is being repeatedly enabled by incoming positive edges from a configurable choice of sampling
clock sources including the System RC oscillator, the 32 KHz crystal oscillator (OSC32K) and
the RC 32KHz oscillator (RC32K). In sampling mode, the BOD18/33 will monitor the
VDDIO/VDDCORE voltages for a very short amount of time before it turns itself off again. Sam-
pling mode is enabled by writing a one to BOD18/33CTRL.MODE. The frequency of the
BOD18/33 one-shot pulses can be varied by the Prescaler Select field in the
BOD18/33SAMPLING register (BOD18/33SAMPLING.PSEL).
/ f_sampling = f_{clk_presc} 2^(PSEL+1)
Since the sampling mode clock is different from the PB clock domain, synchronization among
the clocks is necessary. Figure 12-3 shows a block diagram of the sampling mode. The
BOD18/33 synchronization ready bit in PCLKSR (PCLKSR.BOD18/33SYNRDY) shows the
ready status of the synchronizer. Writing attempts to the BOD18/33SAMPLING register are
ignored while PCLKSR.BOD18/33SYNRDY is zero.
Figure 12-3. Sampling Mode Block Diagram
RCSYS
OSC32K or RC32K
Clk_presc
PRESCALER
fsampling
PSEL
CEN
MODE
CLK_PB
PB
INTERFACE
CSSEL
Unsync
Bus
sync
Bus
SYNCHRONIZER
12.6.3.5
Clock Sources
The clock mux is used to select the clock source for the sampling mode. The clock source is
Enabled/Disabled by the Clock Enable bit in the BOD18/33SAMPLING register
(BOD18/33SAMPLING.CEN). The Clock Source Select bit (BOD18/33SAMPLING.CSSEL) is
used to select the clock source for the sampling mode.
There are two possible clock sources for the sampling prescaler:
42023C–SAM–02/2013
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