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SIM900 GSM/GPRS TTL UART Modem - User Manual
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Page 7
1.1 Turn on GSM Modem Using the PWRKEY Pin (Power on)
You can turn on the Modem by driving the PWRKEY to a low level voltage for a short time (2-3 sec) and then
release. This pin has pulled up to 2.9V in the GSM Modem. The simple circuit illustrates as the following figures.
1K PWRKEY
4.7K
BC547B
Turn on impulse
47K
Fig 6: Turn on GSM Modem using Open collector circuit
1.2 Turn Off GSM Modem
Following ways can be used to turn off the GSM Modem:
•
Normal power down procedure: Turn off GSM Modem using the PWRKEY pin
•
Normal power down procedure: Turn off GSM Modem using AT command
•
Over-voltage or under-voltage automatic shutdown: Take effect if over-voltage or under-voltage is
detected
•
Over-temperature or under-temperature automatic shutdown: Take effect if over-temperature or
under-temperature is detected
1.2.1 Turn Off GSM Modem Using the PWRKEY Pin (Power down)
You can turn off the GSM Modem by driving the PWRKEY to a low level voltage for a short time (2-3 sec) and then
release. Please refer to the turn on circuit above.
The power down scenario illustrates as following fig: 8.This procedure lets the modem 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 GSM Modem will send out result code:
“NORMAL POWER DOWN”
