Turn On The Sim900D Using The Vchg Signal - SimCom SIM900D Hardware Design

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Figure 11: Powered on/down module using transistor
Figure 12: Powered on/down module using button
The power on scenarios is illustrated as following figure.
Figure 13: Timing of power on module
When power on procedure is completed, SIM900D will send following URC to indicate that the module is ready
to operate at fixed baud rate.
RDY
This URC does not appear when autobauding function is active.
Note: User can use AT command "AT+IPR=x" to set a fixed baud rate and save the configuration to non-volatile flash memory.
After the configuration is saved as fixed baud rate, the Code "RDY" should be received from the serial port every time when
SIM900D is powered on. For details, please refer to the chapter "AT+IPR" in document [1].
4.2.1.2

Turn on the SIM900D using the VCHG signal

The SIM900D will be automatically turned on when a charger is connected to the switched-off SIM900D of
which VBAT pin voltage is greater than 3.2V. SIM900D will go into the Charge-only Mode. In this mode, the
module does not register to the network, and has only a few AT commands available. For detailed information
please refer to chapter 3.5.
When module is powered on using the VCHG signal, SIM900D sends out result code as following when fixed
baud rate set:
RDY
CHARGE-ONLY MODE
When user drives the PWRKEY of Charge-only mode SIM900D to a low level voltage for a period of time
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SIM900D_Hardware Design_V2.02 2012-05-07