AT Command Handhook
Last revision 2026/01/24
The article provides a comprehensive guide on using AT commands to control the SIM808 module's power-saving and functionality modes, including sleep mode management and techniques for waking the module, ensuring energy efficiency and optimal performance.
Power Saving Mode
The user can control the SIM808 module to enter or exit sleep mode (AT+CSCLK=1) by DTR signal. When DTR is high level and without interrupt (on air and hardware such as GPIO interrupt or data in serial port), SIM808 will enter sleep mode automatically. In this mode, SIM808 can still receive paging or SMS messages from the network but the serial port is not accessible.
The user must shut off the power supply of GPS, and then the AT commands about the power saving mode can be executed correctly, and current consumption will be lower.
Function Mode
There are three functionality modes, which are set by the AT command AT+CFUN=. The command provides the choice of the functionality levels =0, 1, 4.
| level | Description | Current consumption(uA) |
|---|---|---|
| AT+CFUN=0 | minimum functionality. | 869.5 |
| AT+CFUN=1 | full functionality (default). | 1400 |
| AT+CFUN=4 | flight mode (disable RF function). | 922.5 |
Current consumption of function modes
Minimum functionality mode minimizes the current consumption to the lowest level. If SIM808 is set to minimum functionality by AT+CFUN=0, the RF function and SIM card function will be disabled. In this case, the serial port is still accessible, but all AT commands correlated with RF function and SIM card function will not be accessible.
Sleep Mode (AT+CSCLK=1)
When the GPS function is shut off, the user can control SIM808 module to enter or exit the sleep mode (AT+CSCLK=1) by DTR signal. When DTR is in high level and without interrupt (on air and hardware such as GPIO interrupt or data in serial port), SIM808 will enter sleep mode automatically. In this mode, SIM808 can still receive paging or SMS messages from the network, but the serial port is not accessible.
For SIM808, it requests to set AT command: AT+CSCLK=1 and ensure DTR at high level to enable the sleep mode; the default value is 0, which can not make the module to enter sleep mode.
Wake SIM808 from Sleep Mode
When SIM808 is in sleep mode (AT+CSCLK=1), the following methods can wake it:
- Pull down the DTR pin. The serial port will become active after the DTR pin is pulled to low level for 50ms.
- When a voice or data call is received over the network
- When an SMS message is received over the network
- When an external interrupt is received
- When the VBUS pin is charged
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