Hardware Design V1.01(091226)
Table Of Contents
- Contents
- Version history
- 1 Introduction
- 2 SIM900 Overview
- 3 Application Interface
- 3.1 SIM900 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 SIM Card Interface
- 3.11 LCD Display Interface
- 3.12 Keypad Interface
- 3.13 ADC
- 3.14 Behaviors of the RI
- 3.15 Network Status Indication
- 3.16 General Purpose Input Output (GPIO)
- 3.17 External Reset
- 3.18 PWM
- 3.19 I2C Bus
- 4 Antenna Interface
- 5 Electrical, Reliability and Radio Characteristics
- 6 Mechanics
SIM900 Hardware Design
3.14 Behaviors of the RI
Table 18: 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 1200 ms, then
change to HIGH.
URC Some URCs triggers 1200ms 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 32: SIM900 Services as Receiver
Figure 33: SIM900 Services as caller
3.15 Network Status Indication
The NETLIGHT can be used to drive a network status indication LED lamp. The working state of this pin is
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