EC200U Powers On Successfully but USB Is Not Detected by PC

IoT Modules LTE Standard Module
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1

Hello Support Team,

I am using an EC200U module on a custom hardware design and am experiencing an issue with USB detection.

Observations:

  • The EC200U powers on successfully.

  • The STATUS pin goes high and the STATUS LED turns ON after asserting PWRKEY, indicating that the module has booted.

  • The module remains powered and does not shut down unexpectedly.

  • USB_VBUS is connected to 5 V.

  • USB_DP and USB_DM are connected to the USB connector.

  • When the USB cable is connected to a Windows PC, no new COM ports appear in Device Manager.

  • No unknown USB device or Quectel USB device is detected by Windows.

  • The issue is reproducible on multiple USB ports and cables.

I would appreciate guidance on the following:

  1. Are there any required hardware connections, pull-ups, pull-downs, or configuration pins needed for USB enumeration on the EC200U?

  2. Is there any firmware configuration that could disable the USB interface by default?

  3. Is it possible to verify USB functionality through the debug UART?

  4. Are there recommended checks to confirm that the USB subsystem has initialized correctly after boot?

Please let me know if additional information such as schematics, power measurements, or firmware version is required.

Thank you for your assistance

2

Hi there,
Most probably there is no driver installed in the PC. You can install the driver below based on your PC’s OS.

Windows: Quectel_Windows_USB_Driver(U)_V1.2_EN (1).zip
Linux: Quectel_Linux_USB_Serial_Option_Driver_V1.1.tgz

You can also refer to the Hardware design document as per attached below:

EC200U Reference Design.zip

3

Hello there,

Thank you for your response.

I have already installed the Quectel Windows USB driver on my PC. To verify the driver installation, I connected another EC200U module, and it is detected correctly by Windows with the expected COM ports appearing in Device Manager.

However, the EC200U mounted on my custom hardware is not detected at all. The module powers up correctly, the STATUS pin goes high, and the STATUS LED turns ON after PWRKEY is asserted, indicating that the module has booted successfully. Despite this, Windows does not detect any USB device when the module is connected through USB.

Since the driver and PC setup have been verified using another working EC200U module, I suspect the issue may be related to the hardware design or USB interface initialization on the custom board.

Could you please advise on the following:

  • Are there any specific signals or test points that should be checked to verify USB initialization?

  • Can USB functionality be verified through AT commands on the UART interface?

  • Are there any hardware requirements beyond VBUS, USB_DP, and USB_DM that could prevent USB enumeration?

  • Is there any AT command that can confirm whether the USB interface is enabled in the firmware?

Please let me know if you need anything else from my side.

Thank you for your support.

Best regards,
kazuki

4

Hi there,
Thank you for the detailed explanation.

Since the other EC200U module is working fine, i also suspect the issue might be due to hardware configuration. As the module on your custom board appears to boot normally (STATUS pin high and STATUS LED ON), I recommend checking the following items:

a. Are you able to try to test through UART interface? you can verify the module by testing AT command through the UART and confirming that an “OK” response is received.
b. Check the USB hardware signals:

  • USB_VBUS (pin 71) to check on the VBUS voltage.
  • USB_DP and USB_DM continuity and routing.
  • Please also check whether any abnormal voltage levels are present on the USB_DP and USB_DM pins during power-up.

c. You can also check on the USB interface of your new Hardware design against reference schematic.
d. Is there any difference on the schematic between the current custom board with the one you tested with the good result?

Have a nice day ahead~

5

Hello Firdaus,

Thank you for your suggestions.

I have not yet tested the UART interface on the custom hardware. I will check this as the next step to confirm the module communication status.

For the USB issue, I tested the PC side with another EC200U module and it works correctly with the same USB driver setup. However, the EC200U mounted on my custom board is still not detected by Windows.

When connecting USB from my custom board to the PC, Windows shows:

“Unknown USB Device (Device Descriptor Request Failed)”
Code 43

I checked the following:

  • EC200U powers ON correctly

  • STATUS pin goes HIGH after PWRKEY assertion

  • STATUS LED turns ON

  • USB driver installation has been verified with another working EC200U module

I checked the USB hardware signals:

  • USB_VBUS (pin 71) voltage: 5V

  • USB_DP / USB_DM continuity: OK

  • USB_DP / USB_DM voltage levels during power-up: approximately 0.6V

  • USB routing compared with the reference schematic: matches correctly

Based on these checks, the power supply and USB routing appear normal, but Windows still fails to enumerate the USB device.

Could you please confirm:

  1. Is approximately 0.6V on USB_DP and USB_DM during power-up expected for EC200U before USB enumeration?

  2. Are there any internal USB enable conditions or AT commands that can confirm whether the EC200U USB interface is active?

  3. Does EC200U require any additional hardware connection besides USB_VBUS, USB_DP, and USB_DM for USB enumeration (for example USB_BOOT, RESET, or any control signal)?

  4. Is there any recommended USB signal test procedure or waveform that can confirm whether the module is attempting USB enumeration?

I will also test the UART interface and compare the custom schematic once again with the reference design.

Thank you for your support.

Best regards,
kazuki

6

Hello Firdaus,

Thank you for your suggestions.

I performed further checks on the custom hardware. Currently, the EC200U module powers ON correctly:

  • STATUS pin goes HIGH after PWRKEY assertion

  • STATUS LED turns ON

However, I am facing issues with both USB and UART communication on the custom board.

For USB:
When connecting USB from my custom board to the PC, Windows shows:

“Unknown USB Device (Device Descriptor Request Failed)”
Code 43

I checked the following USB hardware signals:

  • USB_VBUS (pin 71) voltage: 5V

  • USB_DP / USB_DM continuity: OK

  • USB_DP / USB_DM voltage levels during power-up: approximately 0.6V

  • USB routing compared with the reference schematic: matches correctly

For UART:
I also tested the UART interface, but I am not receiving any response from the EC200U module for AT commands.

Since both USB and UART communication are not working, could you please advise what additional checks should be performed?

Could you please confirm:

  1. Is there any hardware condition that can allow the module to power ON and show STATUS LED, but prevent both UART and USB communication?

  2. Are there any required pin states or signals (for example RESET, PWRKEY timing, AP_READY, USB_BOOT, or other control pins) that must be checked?

  3. Is there any way to verify through hardware measurement whether the module has completed booting and is ready for communication?

  4. Are there any recommended test points or signals on the EC200U module to debug UART initialization?

I will also re-check the custom schematic against the reference design and verify all module interface connections.

Thank you for your support.

Best regards,
kazuki

7

Hi there,
Answering the questions:

  1. Yes. The STATUS pin only indicates that the module has entered the power-on sequence. It does not necessarily confirm that the modem firmware has booted successfully. Possible causes include unstable VBAT, RESET_N being asserted
  2. Is there any way to verify through hardware measurement whether the module has completed booting and is ready for communication?
  • Yes you can try to monitor UART_TXD with an oscilloscope or logic analyzer for boot messages or activity during startup. You can also verify that RESET_N remains high and VBAT remains stable throughout the boot process.
  • To confirm whether the module is attempting USB enumeration, monitor USB_DP and USB_DM with an oscilloscope.

You can provide us the schematic design. I can arrange an internal review on it. I will send a follow up email to your email address. Kindly check.

8

Hi Firdaus,

I can provide the schematic design for your review. I have also shared my company details and company email ID with you via email.

We can continue and redirect the conversation through my company email for further discussion.

Thank you.

Best regards,
Kazuki

9

Hi there,
I will proceed to close this ticket in forum.

10

ok Thanks for the help.