First check the level of the STATUS pin to establish whether the module is currently on – if high the module is on, and if low the module is off. If module is already on, you must consider the following two scenarios:

2.1.1 Abnormal communication between PC and EVB

1) Check whether the serial cable is OK. Quectel’s serial cable is recommended as it can avoid abnormal communication between the PC and EVB when using a three-wire serial cable under the hardware flow control.

2) Check that usage of the serial tool is right. If you use the QCOM tool provided by Quectel, please tick RTS as per the figure below:

2.1.2 Abnormal communication between MCU and module

1) Check that the baud rate of the MCU corresponds with that of the module. Quectel modules are set to autobauding by default. Send 2~4 AT commands to synchronize the baud rate of the module (some modules might need more AT commands to achieve synchronization). Once the module is synchronized, we suggest using an AT+IPR command to fix the baud rate and then AT&W to save it.

2) If using three wires to connect the MCU and the module, you should check if the hardware control is closed.