GSM/GPRS Module Series
M35 User Manual
M35_User_Manual Confidential / Released 35 / 85
3.5.4. Summary of State Transition
Table 6: Summary of State Transition
3.6. RTC Backup
The RTC (Real Time Clock) function is supported. The RTC is designed to work with an internal power
supply.
There are three kinds of designs for RTC backup power:
Use VBAT as the RTC power source.
When the module is turned off and the main power supply (VBAT) is remained, the real time clock is still
active as the RTC core is supplied by VBAT. In this case, the VRTC pin can be kept floating.
Use VRTC as the RTC power source.
If the main power supply (VBAT) is removed after the module is turned off, a backup supply such as a
coin-cell battery (rechargeable or non-chargeable) or a super-cap can be used to supply the VRTC pin to
keep the real time clock active.
Use VBAT and VRTC as the RTC power source.
As only powering the VRTC pin to keep the RTC will lead an error about 5 minutes a day, it is
recommended to power VBAT and VRTC pin at the same time when RTC function is needed. The
recommended supply for RTC core circuits are shown as below.
AT+QPOWD, use PWRKEY
pin, or use EMERG_OFF pin
Use AT command
―AT+QSCLK=1‖ and pull
DTR up
Use PWRKEY pin, or use
EMERG_OFF pin
Pull DTR down or
incoming voice call or
SMS or data call
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