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SIM900D Hardware Design
Table21: Pin definition of the GPIO interface
Pin Name
Pin Number
KBR0
10
GPO1
40
*
Note: This function is not supported in the default firmware. There must be customized firmware. Please
contact SIMCom for more details.
3.17 PWM
SIM900D contains one Pulse-Width Modulators (PWM) The PWM is intended 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
ringtones or alert tones. The tone level can be adjusted over a 24 dB range in 4 dB steps, or it can be muted.
Table22: Pin definition of the PWM
Pin Name
PWM
SIM900D_HD_V1.02
Default Function
GPIO8
GPIO1
Pin Number
47
Pulse-Width Modulator Signal
Default State
Output Pull down
Output Pull down
49
09.04.2010
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