SIM900 Hardware Design
PWRKEY
STATUS
Turn Off
Delay > 500ms
Restart
3.5 Power Saving
Figure 14: Timing of restart system
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 hardware interface signal can be used to lead system to be in
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;
If SIM900A 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 SIM900A 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.
After SIM900A has been set by “AT+CFUN=0” or “AT+CFUN=4”, it can return to full functionality by
“AT+CFUN=1”.
For detailed information about “AT+CFUN”, please refer to document [1].
3.5.2 Sleep Mode (Slow Clock Mode)
We can control SIM900A module to enter or exit the SLEEP mode in customer applications through DTR signal.
When DTR is in high level and there is no on air and hardware interrupt (such as GPIO interrupt or data on serial
port), SIM900A will enter SLEEP mode automatically. In this mode, SIM900A can still receive paging or SMS
from network but the serial port is not accessible.
Note: For SIM900A, it requests to set AT command “AT+CSCLK=1” to enable the sleep mode; the default
value is 0, that can’t make the module enter sleep mode. For more details please refer to our AT command list.
SIM900_HD_V1.01
29
26.12.2009