SIM900D Hardware Design
3.6.1 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 SIM900D 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 SIM900D 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 SIM900D 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].
3.6.2 Sleep Mode (Slow Clock Mode)
The SIM900D can be controlled 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), SIM900D will enter SLEEP mode automatically. In this mode, SIM900D can still receive paging or SMS
from network but the serial port is not accessible.
Note: For SIM900D, 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.
3.6.3 Wake Up SIM900D from SLEEP Mode
When SIM900D is in SLEEP mode, the following methods can wake up the module.
z
Enable DTR pin to wake up SIM900D.
If DTR pin is pulled down to a low level
，
this signal will wake up SIM900D from power saving mode. The
serial port will be active after DTR changed to low level for about 50ms.
z
Receiving a voice or data call from network to wake up SIM900D.
z
Receiving a SMS from network to wake up SIM900D.
3.7 Summary of State Transitions (except SLEEP mode)
The following figure shows how to proceed from one mode to another.
SIM900D_HD_V1.02
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