I 2 C Bus; Antenna Interface - SIM Tech SIMCom SIM900-DS Hardware Design

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Figure 34: Reset timing
This pin is already pulled up in the module, so the external pull-up resistor is not necessary. A 100nF capacitor
close to the NRESET pin is strongly recommended. A reference circuit is shown in the following figure.
Figure 35: Reset reference design circuit
NOTE: It is recommended to cut off the VBAT power supply directly instead of using external reset pin when SIM900-DS can
not respond to the AT command "AT+CPOWD=1" and PWRKEY pin.
2
4.15 I C Bus
2
The SIM900-DS provides an I C interface which is only used in the embedded AT application.
Note: This function is not supported in the standard firmware. If user wants this function, the firmware must be customized.
Please contact SIMCom for more details.

4.16 Antenna Interface

SIM900-DS provides a RF antenna interface. The 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 controlled in 50Ω. To facilitate the antenna tuning and certification test, a RF connector and an antenna
matching circuit should be added. The following figure is the recommended circuit.
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SIM900-DS_Hardware Design_V1.00 2013-01-20