SimCom SIM900D EVB, Проектирование аппаратного обеспечения

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SIM900D Hardware Design
This result code does not appear when autobauding is active.
3.4.1.2 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 3.3V. 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
(please refer to
Figure 9 Timing of turn on system using PWRKEY
), the SIM900D will power up and go into
Charge mode during normal operation. In this case, SIM900D sends out result code as following:
From CHARGE-ONLY MODE to NORMAL MODE
In Charge mode during normal operation, all operations and AT commands are available.
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)
User can turn off the SIM900D by driving the PWRKEY to a low level voltage for a short time and then release
(Please refer to the turn on circuit).
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 not 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.
The power down scenario illustrates as following figure.
SIM900D_Hardware Design_V1.04 2010.10.09
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