EC20 mini pcie problem with uart interface

Hi, I’m trying to connect EC20 mini pcie module with MCU STM32F103 via uart interface. I’m getting problem with EC20 module, it not respond anything when I send AT command. When I plug power supply I can see led wwan status toggle normal and I can call to module. I tested EC20 module with USB interface, it working normal.
Pls help me fix this problem !

Dear Linh Bui,
Thanks for your inquiry in Quectel forum.
About your issue, could you help to confirm the following information:
1.whether you use the correct board to connect EC20 MINIPCIE module;
2.please know that EC20 is used in China marketing, normally it named EC20 minipcie-c module, you can see the label in the bottom of the module.
3. Please confirm the UART level is matched between module and your MCU.

Hi Kyson,
My EC20 module: EC20CEHCLG-128-SNNS
All module pin correctly, power supply 3.3V
UART interface level 3V3 ??? .
I read in file Quectel_EC20_Mini_PCIe_Hardware_Design_V1.1, it show UART level 3V3, but measurement by ossilocope and DMM it show only 1V8. I think that problem.
Pls confirm it correct !

Please check the following difference between MINIPCIE and MINIPCIE-C module, they have different UART power domain. Please note that EC20 module is apply for China domestic marketing, they are all MINIPCIE-C module, you can check the label at the bottom of the module. So i think you may use MINIPCIE-C module, not MINIPCIE module. Please check it. Thanks!

This is my EC20 module. So I get mistake :joy:
May I have hardware design guide for this module?

Please check the following document. Thanks!
Quectel_EC20_R2.1_Mini_PCIe-C(Audio)_Hardware_Design_V1.0.pdf (835.5 KB)

Hi Keyson,
Thank you very much for your time and your guidance.