Sleep Mode 2 (At+Csclk=2); Wake Up Sim900B From Sleep Mode 2 (At+Csclk=2); Rtc Backup - SimCom SIM900B Hardware Design

Receive a voice or data call from network.
Receive a SMS from network.
3.4.4

Sleep Mode 2 (AT+CSCLK=2)

In this mode, SIM900B will continuously monitor the serial port data signal. When there is no data transfer over 5
seconds on the RXD signal and there is no on air and hardware interrupts (such as GPIO interrupt), SIM900B will
enter sleep mode 2 automatically. In this mode, SIM900B can still receive paging or SMS from network but the
serial port is not accessible.
Note: For SIM900B, It is requested to set AT command "AT+CSCLK=2" to enable the sleep mode 2; the default value is 0, which
can not make the module to enter sleep mode. For more details please refer to document [1].
3.4.5

Wake Up SIM900B from Sleep Mode 2 (AT+CSCLK=2)

When SIM900B is in sleep mode 2 (AT+CSCLK=2), the following methods can wake up the module:
Send data to SIM900B via main serial port.
Receive a voice or data call from network.
Receive a SMS from network.
Note: The first byte of the user's data will not be recognized.
3.5

RTC Backup

Current input for RTC when the VBAT is not supplied for the system. Current output for backup battery when
the VBAT power supply is in present and the backup battery is in low voltage state. The RTC power supply of
the module can be provided by an external capacitor or a battery (non-chargeable or rechargeable) through the
VRTC. The following figures show various reference circuits for RTC back up.
External capacitor backup
Non-chargeable battery backup
SIM900B_Hardware Design_V2.01
*
Figure 11: RTC supply from capacitor
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Smart Machine Smart Decision
2012-05-07