SIM Tech SIMCom SIM800, Проектирование аппаратного обеспечения

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SIM800_Hardware Design_V1.09 27 2016-06-30
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
RTC
Core
1.5K
Module
VRTC
Large-capacitance
Capacitor
Figure 16: RTC supply from capacitor

Non-chargeable battery backup
RTC
Core
1.5K
Module
VRTC
Non-chargeable
Backup Battery
Figure 17: RTC supply from non-chargeable battery