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decides the voltage range for the BOD, while BUENTHRES is used for tuning of the BOD threshold.
Refer to Section 10.3.4.5 (p. 113) for details regarding BOD calibration.
Note
BUVINPEN in EMU_ROUTE is by default set. If Backup mode is not to be used, this bit
should be cleared.
Note
The voltage on BU_VIN has to be above the threshold for the BOD sensing on BU_VIN to
enter backup mode.
The BU_STAT pin can be used to indicate whether or not the system is in backup mode. To enable
exporting of the backup mode status, set STATEN in EMU_BUCTRL. The BU_STAT pin is driven to
BU_VIN when backup mode is active and to ground otherwise.
10.3.4.4 Leaving backup mode
To exit backup mode, the voltage on VDD_DREG has to be above the threshold programmed in
EMU_BUACT. BUEXRANGE decides the voltage range for backup mode exit, while BUEXTHRES is
used for tuning. When leaving backup mode, a system reset is triggered, resetting everything except the
backup domain. When backup mode has been active, the BURST bit in EMU_RSTCAUSE is set.
Figure 10.4. Entering and leaving backup mode
EMU_BUACT_BUEXRANGE /
EMU_BUACT_BUEXTHRES
VDDREG
EMU_BUINACT_BUENRANGE /
EMU_BUINACT_BUENTHRES
Backup m ode active
Tim e
Figure 10.4 (p. 113) illustrates how the BOD sensing on VDD_DREG can be programmed to
implement hysteresis on entering and exiting backup mode.
10.3.4.5 Threshold calibration
The thresholds for entering and exiting backup mode are configured in the EMU_BUINACT and
EMU_BUACT registers, respectively. Calibration of these thresholds is performed during production
test, but may also be performed using the DAC. The calibration values for the BODs sensing on
unregulated power and BU_VIN, BUBODUNREG and BUBODBUVIN respectively, are available in
EMU_BUBODVINCAL and EMU_BUBODUNREGCAL. These registers are written during production
test and should not be modified except for calibrating the Backup BOD sensing on VDD_DREG, as
described in the following section.
Setting BODCAL in EMU_BUCTRL will enable a mode where the BOD is sensing the DAC output, as
depicted in Figure 10.5 (p. 114) . For the BODCAL bit to take effect, the backup power enable bit, EN
in EMU_BUCTRL, has to be cleared. The procedure for BOD calibration is as follows:
• Clear EN and set BODCAL in EMU_BUCTRL.
• Store the values in EMU_BUBODVINCAL and EMU_BUBODUNREGCAL before clearing these
registers.
• Configure the DAC to output to the maximum level and wait for 500 us before configuring the DAC
output to the wanted BOD trigger voltage level.
• Step through the BOD calibration values (RANGE and THRES in EMU_BUINACT) with 500 us delay in
between steps until the BUBODVDDDREG flag in RMU_RSTCAUSE is set. The RANGE and THRES
2013-05-08 - Wonder Gecko Family - d0233_Rev0.50
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