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SIM900 GSM/GPRS TTL UART Modem - User Manual
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After this moment, the AT commands can’t be executed. The modem enters the POWER DOWN mode. POWER
DOWN can also be indicated by STATUS pin, which is a low level voltage in this mode.
1.3 Turn Off GSM Modem Using AT Command
You can use the AT command “AT+CPOWD=1” to turn off the modem. This command lets the GSM Modem log off
from the network and allows the GSM Modem 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”
After this moment, the AT commands can’t be executed. The GSM Modem 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.
1.4 Restart GSM Modem Using the PWRKEY Pin
You can restart GSM MODEM by driving the PWRKEY to a low level voltage for a short time(2-3 sec) and then
release, the same as turning on GSM MODEM using the PWRKEY pin. Before restarting the GSM MODEM, you
need delay at least 500ms from detecting the STATUS low level on. The restarting scenario illustrates as the
following figure.
1.5 Power Saving
There are two methods for the GSM Modem to enter into low current consumption status. “AT+CFUN” is used to
set GSM Modem into minimum functionality mode and DTR hardware interface signal can be used to lead system
to be in SLEEP mode (or slow clocking mode).
1.6 Minimum Functionality Mode
Minimum functionality mode reduces the functionality of the GSM Modem to a minimum and, thus, minimizes the
current consumption to the lowest level. This mode is set with the “AT+CFUN” command which provides the
choice of the functionality levels <fun>=0，1，4
•
0: minimum functionality;
•
1: full functionality (default);
•
4: disable phone both transmit and receive RF circuits;
If GSM MODEM has been set to minimum functionality by “AT+CFUN=0”, the RF function and SIM card function
will be closed. In this case, the serial port is still accessible, but all AT commands correlative with RF function or
SIM card function will not be accessible.
If GSM MODEM has been set by “AT+CFUN=4”, the RF function will be closed, the serial port is still active. In this
case all AT commands correlative with RF function will not be accessible.
