Huawei ME909 Series Hardware Manual page 17

HUAWEI ME909 Series Mini PCIe Module
Hardware Guide
Figure 3-5 Connections of the RESIN_N pin
As the RESIN_N signal are relatively sensitive, it is recommended that you install a 10
nF to 0.1 µF capacitor near the RESIN_N pin of the interface for filtering. In addition,
when you design a circuit on the PCB of the interface board, it is recommended that
the circuit length should not exceed 20 mm and that the circuit should be kept at a
distance of 2.54 mm (100 mil) at least from the PCB edge. Furthermore, you need to
wrap the area adjacent to the signal wire with a ground wire. Otherwise, the module
may be reset due to interference.
The ME909 module supports hardware reset function. If the software of the ME909
module stops responding, you can reset the hardware through the RESIN_N signal as
shown in‎ F igure 3-6 . When a low-level pulse is supplied through the RESIN_N pin, the
hardware will be reset. After the hardware is reset, the software starts powering on the
module and reports relevant information according to the actual settings. For example,
the AT command automatically reports ^SYSSTART.
Figure 3-6 Reset pulse timing
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Issue 0.1 (2013-06-09)
The RESIN_N pin must not be pulled down for more than 1s.
The RESIN_N pin is optional, which can be not connected.
The maximum Forward Voltage Drop of the diode used in the module is 0.6 V.
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Description of the Application Interfaces
17