Behaviors Of The Ri - SimCom SIM900D Hardware Design

SIM900D Hardware Design

3.14 Behaviors of the RI

Table21: Behaviours of the RI
State RI respond
Standby HIGH
Voice calling Change LOW, then:
（1）Change to HIGH when the call is established.
（2）Use AT command ATH, the RI pin will be changed to HIGH.
（3）When sender hangs up, it will be changed to HIGH.
Data calling Change LOW, then：
（1）Change to HIGH when the call is established.
（2）Use AT command ATH, the RI will be changed to HIGH.
SMS Change to low and hold low level for about 120 ms when the module receive a SMS, and then
it is changed to HIGH.
URC Some URCs triggers 120ms low level on RI. For more details, please refer to related
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 the ring.
SIM900D_Hardware Design_V1.04
Figure29: RI behaviour of voice calling as a receiver
Figure30: RI behaviour of data calling as a receiver
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2010.10.09