SIM900 Hardware Design
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 33: SIM900 Services as Receiver
RI
Power on calling Hang up Echo talking
calling Echo Hang up
HIGH
LOW
Figure 34: 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
listed in following table:
Table
19: Working state of the NETLIGHT
State SIM900 function
Off SIM900 is not running
64ms On/ 800ms Off SIM900 does not find the network
64ms On/ 3000ms Off SIM900 find the network
64ms On/ 300ms Off GPRS communication
We provide a reference circuit for you, shown as following figure:
SIM900_HD_V1.05 06.23.2010
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