SIM900D Hardware Design
3.4.1.2 Turn on the SIM900D using the VCHG signal
As described in chapter 3.4, charger can be connected to SIM900D’s VCHG Pin regardless of the module’s
operating mode.
If the charger is connected to the module’s VCHG Pin while SIM900D is in POWER DOWN mode, SIM900D
will go into the Charge-only Mode (Off and charging). In this mode, the module will not register to network, and
only a few AT commands can work in this mode. For detailed information please refers to chapter 3.5.
When module is powered on using the VCHG signal, SIM900D sends out result code as following when fixed
baud rate:
RDY
CHARGE-ONLY MODE
In Charge-only mode, by driving the PWRKEY to a low level voltage for period time (Please refer to the power
on scenarios in 3.4), SIM900D will power up and go into charge mode (charging in normal mode), all operation
and AT commands can be available. In this case, SIM900D will send out result code as following:
From CHARGE-ONLY MODE to NORMAL MODE
3.4.2 Turn Off SIM900D
Following ways can be used to turn off the SIM900D:
z
Normal power down procedure: Turn off SIM900D using the PWRKEY pin
z
Normal power down procedure: Turn off SIM900D using AT command
z
Over-voltage or under-voltage automatic shutdown: Take effect if over-voltage or under-voltage is detected
z
Over-temperature or under-temperature automatic shutdown: Take effect if over-temperature or
under-temperature is detected.
3.4.2.1 Turn Off SIM900D Using the PWRKEY Pin (Power down)
The SIM900D can be turned off by driving the PWRKEY to a low level voltage for a short time and then release.
Please refer to the turn on circuit. The power down scenario illustrates as following figure.
This procedure lets the module log off from the network and allows the software to enter into a secure state and
save data before completely disconnecting the power supply.
Before the completion of the switching off procedure the module will send out result code:
NORMAL POWER DOWN
After this moment, the AT commands can’t be executed. The module enters the POWER DOWN mode, only the
RTC is still active. POWER DOWN can also be indicated by STATUS pin, which is a low level voltage in this
mode.
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