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ULINK: no target connection with ULINKpro Isolation Adapter

Information in this knowledgebase article applies to:

  • ULINKpro Isolation Adapter


I want to use an ULINKpro with an Isolation Adapter and my target hardware. But this fails, because with the Isolation Adapter I can't establish a connection to the device in Serial Wire debug mode. Without the Isolation Adapter I have a proper connection. Is the Isolation Adapter broken? Or what is the problem?


One known rare issue is, that some devices fail to sink the required amount of current on the SWDIO pin.

For each direction the Isolation Adapter has a separate digital isolator, which must be combined on both ends. While the host->target direction outputs high, the devices needs to drive low against this via a series resistor on the Isolation adapter for a short period of time, until the target->host direction detects the low and switches the state. If the device does not manage to drive the signal below the low-level of the Isolation adapter, this mechanism does not work.

This effect can be seen on the following oscilloscope screenshots, which show the beginning of the communication on the SWDIO pin at the target side:

begin of communication
This shows the start of the communication on the SWDIO line (target side).

target drives not below low-level
This is the right part of the first picture zoomed-in. Here the target tries to drive the SWDIO signal low but gets the signal level down to just about half of the high level.

The Isolation Adapter fails to detect the direction of this bi-directional data signal and the low output of the target is not forwarded to the host. The communication fails.

Known devices with that problem are:

  • NXP Kinetis KE02, KE04, KE06


Unfortunately, there is no known solution. If you have a device showing this problem, the ULINKpro Isolation Adapter can't be used with it.



Last Reviewed: Tuesday, April 4, 2017

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