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