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µVISION DEBUGGER: Cannot connect to J-Link via USB.

Information in this knowledgebase article applies to:

  • J-Link and J-Trace debugger


When I try to debug an ARM7/9 device with the µVision Debugger via J-Link, starting a debug session or a flash download always fails with the following message in the Build Output window:

Cannot connect to J-Link via USB.


The J-Link device is probably configured for a J-Link USB ID other than 0. Due to that, it can't be recognized by the µVision J-Link Debugger driver used for ARM7/9 devices.


Configure the J-Link for USB ID 0. This can be done with the J-Link commander tool found in the MDK-ARM installation directory C:\Keil\ARM\Segger\JLink.exe. This will identify the J-Link with ID different than 0 and when connected, provides a command "usbaddr" to change the ID:

SEGGER J-Link Commander V4.36l ('?' for help)
Compiled Dec 2 2011 18:52:52
DLL version V4.40c, compiled Jan 24 2012 09:30:33
Firmware: J-Link ARM V6 compiled Feb 1 2011 14:28:14
Hardware: V6.00
S/N: ********
Feature(s): FlashBP, FlashDL
J-Link>usb 0
/* old style: J-Link>usbaddr=0 */
USB address successfully changed to '0'.
Please unplug the device, then plug it back in.

After reconnecting the J-Link unit to the PC, debugging the ARM7/9 device with J-Link via the µVision Debugger should work.

Please note that the µVision J-Link Debugger driver used for Cortex-M devices has the ability to use J-Link adapters with different USB IDs. The ID can also be changed with J-Link Setup dialog.



The following Discussion Forum threads may provide information related to this topic.

Last Reviewed: Monday, September 26, 2016

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