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SIM900D Hardware Design
Normal Mode
Normal Mode
3.8 RTC Backup
The RTC (Real Time Clock) power supply of module can be provided by an external capacitor or a battery
(rechargeable or non-chargeable) through the VRTC.
Note: If the RTC function is enabled, a battery or capacitor should be connected with the VRTC pin.
Otherwise the VRTC pin can be keep open.
The following figures show various sample circuits for RTC backup.
Non-chargeable
Backup Battery
SIM900D_HD_V1.02
AT+CPOWD or
PWRKEY
PWRKEY
Charge-only
Charge-only
Mode
Mode
State Transition
Figure12:
Figure13: RTC supply from non-chargeable battery
Power Down
Power Down
Mode
Mode
Insert charger
Module
10K
VRTC
34
RTC
Core
09.04.2010
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