SimCom SIM900 Operation User's Manual page 3

9. Network Indicator LED: Network Status Indicator LED.
State
Off
64ms On/ 800ms Off
64ms On/ 3000ms Off
64ms On/ 300ms Off
10. ADC and PWM Pins: ADC and PWM Pins of SIM900A.(Refer page 9,10 for ADC and PWM
commands)
11. Audio Interface: Audio Pins (Speaker and microphone pins) of SIM900/900A.
12. SIM Interface: SIM Card holder Interface.
13. Vout: Regulated 4.2V output voltage for external application circuit.
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SIM900 function
SIM900 is not running
SIM900 does not find the network
SIM900 find the network
GPRS communication