Behaviors Of The Ri - SIM Tech SIM900D HD Manual

SIM900D Hardware Design

3.14 Behaviors of the RI

Table19: 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.
RI
HIGH
LOW
Power on
HIGH
calling
LOW
SIM900D_HD_V1.02
Ring
Ring
MO or MT
Hang up
Figure26: SIM900D Services as Receiver
talking
Whenever occurs, it will keep high.
Figure27: SIM900D Services as caller
Hang on MO or
(talking)
MT
Hang up
47
Ring
calling
09.04.2010