Sleep Mode (At+Csclk=1); Wake Up Sim800 From Sleep Mode (At+Csclk=1); Rtc Backup - SimCom SIM800 Hardware Design

be accessible.
For detailed information about the AT Command "AT+CFUN=<fun>", please refer to document [1].
4.3.2.

Sleep Mode (AT+CSCLK=1)

User can control SIM800 module to enter or exit the sleep mode (AT+CSCLK=1) by DTR signal. When DTR
is in high level and without interrupt (on air and hardware such as GPIO interrupt or data in serial port),
SIM800 will enter sleep mode automatically. In this mode, SIM800 can still receive paging or SMS from
network but the serial port is not accessible.
Note: Autobauding is the default setting. Module can not enter sleep mode if the baud rate of MCU's serial port
not synchronous with module after module power on.
4.3.3.

Wake Up SIM800 from Sleep Mode (AT+CSCLK=1)

When SIM800 is in sleep mode (AT+CSCLK=1), the following methods can wake up the module:

Pull down DTR pin.
The serial port will be active after DTR pin is pulled to low level for about 50ms.

Receive a voice or data call from network.

Receive a SMS from network.

Receive external interrupt

4.4. RTC Backup

VRTC is an input pin when the VBAT is not supplied by external power. When the VBAT power supply is in
present and the backup battery is in low voltage state, VRTC can charge the backup battery. The RTC power
supply of module can be provided by an external capacitor or a battery (non-chargeable or rechargeable) through
the VRTC. The following figures show various reference circuits for RTC back up.

External capacitor backup
Large-capacitance
Capacitor
SIM800_Hardware Design_V1.10
VRTC
Figure 16: RTC supply from capacitor
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2018-08-13