User's Manual

SIM900B Hardware Design
DOWN mode, and only the RTC is still active. POWER DOWN can also be indicated by VDD_EXT pin, which
is a low level voltage in this mode.
To monitor the temperature, the “AT+CMTE” command can be used to read the temperature when the module is
power on.
For details please refer to document [1]
3.4.3 Restart SIM900B Using the PWRKEY Pin
By driving the PWRKEY to a low level voltage for a short time and then release ,SIM900B can be restarted, the
timing is the same as turning on SIM900B using the PWRKEY pin. Before restarting the SIM900B, you need
delay at least 500ms from detecting the VDD_EXT low level on. The restarting scenario illustrates as the
following figure.
VDD_EXT
（OUTPUT）
H
PWRKEY
（INPUT）
Delay > 500ms
Turn off
Pull down the PWRKEY
to turn on the module
Restart
Figure 10: Timing of restart system
3.5 Power Saving
There are two methods for the module to enter into low current consumption status. “AT+CFUN” is used to set
module into minimum functionality mode and DTR signal can be used to control system enter or exit SLEEP
mode (or slow clocking mode).
3.5.1 Minimum Functionality Mode
Minimum functionality mode reduces the functionality of the module 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
z 0: minimum functionality;
z 1: full functionality (default);
z 4: disable phone both transmit and receive RF circuits;
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