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
3.15 Behaviors of the RI
Table 19: Behaviours of the RI
State RI respond
Standby
HIGH
Voice calling Change LOW, then:
（1）Change to HIGH when establish calling.
（2）Use AT command ATH, the RI pin changes to HIGH.
（3）Sender hangs up, change to HIGH.
Data calling Change LOW, then：
（1）Change to HIGH when establish calling.
（2）Use AT command ATH, the RI changes to HIGH.
SMS When receive SMS, The RI will change to LOW and hold low level about 120 ms, then
change to HIGH.
URC Some URCs triggers 120ms low level on RI. For more details, please refer to document [10]
If the module is used as caller, the RI will maintain high. However, when it is used as receiver, following is timing
of ring.
Power on Ring
MO or MT
Hang up
Ring
Hang on
(talking)
MO or
MT
Hang up
Ring
RI
HIGH
LOW
Figure 29: SIM900B Services as Receiver
RI
Power on calling Hang up Echo talking
calling Echo Hang up
HIGH
LOW
Figure 30: SIM900B Services as caller
3.16 Network Status Indication
The NETLIGHT can be used to drive a network status indication LED lamp. The working state of this pin is
listed in following table:
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