Hello,
I am using the Quectel UMTS<E EVB Kit with an Quectel EC912U-GL module and I am trying to communicate with the module using an external MCU instead of the onboard USB-UART interface.
I connected my external MCU UART lines to the RX/TX pairs on J806 (both the 1.8V and 3V UART pins were tested separately).
My issue is that the communication is unstable:
-
Sometimes AT commands work correctly
-
Sometimes I receive corrupted characters
-
Sometimes there is no response at all
-
Communication becomes inconsistent after some time
Example behavior:
-
Module boots correctly
-
I can see responses such as
+CFUN: 1 -
Sometimes I also see
+CPIN: NOT READY -
But when sending
AT, I occasionally receive corrupted characters instead ofOK
I would like to understand:
-
Are the J806 UART pins intended for direct communication with an external MCU?
-
Are these lines shared with the onboard USB-UART converter and causing bus contention?
-
Do any jumpers/switches need to be changed to fully isolate the onboard USB-UART path?
-
Is there any required level shifting, buffering, or flow control configuration for stable communication?
-
Without modifying the EVB hardware (cutting traces/removing components), what is the recommended way to reliably communicate with the module from an external MCU?
My current setup:
-
External MCU UART TX → J806 RX
-
External MCU UART RX → J806 TX
-
Common GND connected
-
Tested baud settings: [write your baud rates here]
-
Tested both 1.8V and 3V UART headers
Has anyone successfully used this EVB with an external MCU in a stable way? If yes, which UART pins/jumper settings were used?
Thanks.