"No communications link..." error message - please help!

Hello, when we hit compile and download we keep getting the error message:

“No communications link available to VEX device. Check that your device is connected to the PC.”

This happens on a regular basis on multiple laptops and cortexes. After a while it will always start working correctly for no apparent reason. Any suggestions? Thanks!

Hello grepin,

Assuming you are using easyC V4, such message usually means you need to re-download the firmware into the Microcontroller.

If the error message appears again, please take a screenshot and post in in the forum. Once I have the screenshot I should be able to provide you with further assistance.


If you are seeing this error message in ROBOTC, there are a couple of things I can suggest checking that may resolve this issue.

The biggest cause of this problem is removing the Cortex from the computer while the Program Debug window is open. Generally, you will want to close the Program Debug window before disconnecting the Cortex from the computer, as this will ensure that the connection between the PC and the Cortex is shut down properly; otherwise, ROBOTC may still be trying to communicate with the Cortex.

Next, try redownloading the firmware to the Cortex microcontroller. This can be done through the ‘Robot -> Download Firmware -> Automatically Update VEX Cortex’ menu option.

Finally, try different USB ports (such as ports on the back of the computer) to see if this issue is tied to a specific bank of USB ports.

If none of this works, please let us know what the Cortex appears as in the Windows Device Manager (when the error message occurs) as this should help with the debugging process.

Thanks in advance!