Hardware Design V1.01(091226)

SIM900 Hardware Design
3.18 PWM
SIM900 contains two DC Pulse-Width Modulators (PWMs) which can be used in conjunction with an external
transistor for driving a vibrator, or a backlight LED for illuminating an LCD display or keyboard.
Each PWM features 7-bit resolution and a maximum conversion rate is 3.25 MHz. Each PWM uses two 7-bit
unsigned binary numbers: one for the output period and one for the pulse width or the duty cycle.
Table 21: Pin define of the PWM
Pin Name Pin Number
PWM1 35 Pulse-Width Modulator Signal
PWM2 36 Pulse-Width Modulator Signal
Note: This function is not supported in the default firmware. There must be customized firmware if you want.
Please contact SIMCom for more details.
3.19 I2C Bus
The SIM900 initiates a data transfer on the bus and generates the clock signal to execute the transfer. The
features include the following:
z Maximum output rate equal to 400 kbit/s
z Open-drain outputs
z Automatic Start and Stop generation
z Automatic acknowledge generation and checking
z Automatically generates Start repeated pattern when performing read operations
z Automatically observes and generates the acknowledge bit
z Implements a hardware assisted I2C-bus protocol
z Supports 8-bit, 16-bit, and 32-bit accesses on the MCU peripheral bus
Table 22: Pin define of the I2C Bus
Pin Name Pin Number Function
SCL 38 I2C Bus Clock
SDA 37 I2C Bus Data
Note: This function is not supported in the default firmware. There must be customized firmware if you want.
Please contact SIMCom for more details.
4 Antenna Interface
SIM900 provides RF antenna interface. And customer’s antenna should be located in the customer’s main board
and connect to module’s antenna pad through microstrip line or other type RF trace which impendence must be
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