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Information in this article applies to:

  • ULINK USB-JTAG Adapter


I have problems when I start debugging using the Keil ULINK USB-JTAG Adapter. The ULINK driver displays the message:

JTAG Communication Failure

What can cause this error? Is this a problem with the Embedded ICE of the ARM device?


This message may have several reasons that are listed below:

  • The Embedded ICE or the JTAG Interface on the ARM device might be disabled.
  • The power supply of the ULINK driver might be incorrect. Open ULINK and set the jumper VCC to 3.3V. For more information refer to the Getting Started User's Guide, JTAG Debugging - ULINK: Interface Schematic.
  • The ARM device may execute some code that interrupts communication with the Embedded ICE. This happens when the device executes random code. Some devices have also problems with the JTAG interface, when the device goes into IDLE mode. To recover such devices, you may erase the complete program using serial program utilities.
  • Enable the option Project - Options - Debug - ULINK ARM Debugger Settings - Use Reset at Startup. This ensures that the ARM device gets a proper reset signal at startup.
  • When ARM devices work with a slow clock (below 6MHz) the ULINK may be too fast by default. Reduce the MAX JTAG Clock in the dialog Project - Options - Debug - ULINK ARM Debugger Settings.
  • For ULINK2 adapters, you may receive this message if you use the adapter on more than 1 PC and the PC's have different versions of µVision. New versions of µVision may require an update to the firmware in the ULINK2 adapter, and older versions may not work with that update.

    Before µVision updates the ULINK2 firmware, it displays a warning message that allows you to cancel the firmware update. If you allow the firmware update, remember to update the PC with the older version so the ULINK2 adapter can be used on both PCs.


  • Getting Started User's Guide, JTAG Debugging



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

Last Reviewed: Thursday, April 9, 2009

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