SIM900D Hardware Design
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MODULE
NETLIGHT
VBAT
Figure33: Reference circuit of NETLIGHT
3.16 General Purpose Input Output (GPIO)
SIM900D provides a limited number of General Purpose Input/Output signal pin. The output and input voltage
level of the GPIO can be set by AT command.
For more details, please refer to
related document [1]
Table23: Pin definition of the GPIO interface
Pin Name
Pin Number
Default Function
Second Function
Default State
KBR0
10
GPIO8
SIM card detection
Output Pull down
GPO1
40
GPIO1
Output Pull down
The SIM card detection function can be implemented, please refer to 3.11 SIM interface for more details.
3.17 PWM
SIM900D contains one Pulse-Width Modulators (PWM) which can be used for controlling a buzzer.
Features of buzzer PWM:
10-bit resolution for buzzer tone frequency generation from 200 Hz to 5 kHz
Tone frequency error < 1 % for all standard piano notes from 200 Hz to 5 kHz
Tone level control from 0 dB down to
−
24 dB in +4 dB steps
Audio mute
The PWM for the buzzer outputs a square wave at the desired tone frequency. The tone frequencies are
programmable from 200 Hz to 5 kHz and can be re-programmed on-the-fly to generate monophonic audio
SIM900D_Hardware Design_V1.04
2010.10.09
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