User's Manual
Table Of Contents
- Contents
- Version history
- 1 Introduction
- 2 SIM900B Overview
- 3 Application Interface
- 3.1 SIM900B Pin Description
- 3.2 Operating Modes
- 3.3 Power Supply
- 3.4 Power Up and Power Down Scenarios
- 3.5 Power Saving
- 3.6 Summary of State Transitions (except SLEEP mode)
- 3.7 RTC Backup
- 3.8 Serial Interfaces
- 3.9 Audio Interfaces
- 3.10 Buzzer
- 3.11 SIM Card Interface
- 3.12 LCD Display Interface
- 3.13 Keypad Interface
- 3.14 ADC
- 3.15 Behaviors of the RI
- 3.16 Network Status Indication
- 3.17 General Purpose Input Output (GPIO)
- 4 Antenna Interface
- 5 Electrical, Reliability and Radio Characteristics
- 6 Mechanics
SIM900B Hardware Design
If SIM900B 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 SIM900B 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 SIM900B 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)
DTR signal can be used to control SIM900B module to enter or exit the SLEEP mode in customer applications
When DTR is in high level and there is no on air and hardware interrupt (such as GPIO interrupt or data on serial
port), SIM900B will enter SLEEP mode automatically. In this mode, SIM900B can still receive paging or SMS
from network but the serial port is not accessible.
Note: For SIM900B, 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.
3.5.3 Wake Up SIM900B from SLEEP Mode
When SIM900B is in SLEEP mode, the following methods can wake up the module.
z Enable DTR pin to wake up SIM900B.
If DTR pin is pulled down to a low level，this signal will wake up SIM900B 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 SIM900B.
z Receiving a SMS from network to wake up SIM900B.
3.6 Summary of State Transitions (except SLEEP mode)
The following figure shows how to proceed from one mode to another.
Normal Mode
Normal Mode
Power Down
Mode
Power Down
Mode
AT+CPOWD or Drive
PWRKEY to ground
Drive PWRKEY to ground
Figure 11:
State Transition
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