SIM900D Hardware Design
Table21: Pin definition of the GPIO interface
Pin Name
Pin Number
Default Function
Default State
KBR0
10
GPIO8
Output Pull down
GPO1
40
GPIO1
Output Pull down
*
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
Pin Number
PWM
47
Pulse-Width Modulator Signal
SIM900D_HD_V1.02
09.04.2010
49
