J-Link cannot connect to the CPU

There are many different scenarios, which may prevent the J-Link from establishing a successful connection to the target device. The following article refers to the different scenarios and provides information on how to trouble shoot and in the next step how to fix them. In general, we recommend to verify the correct connection between J-Link and the target device using the diagnostic utility J-Link Commander before moving to the actual environment (e.g. Embedded Studio IDE). Therefore, this article refers to J-Link Commander and assumes that the latest J-, only. We recommend to work through this article from the beginning to the end.

Requirements:

• J-Link
• Target
• Latest J-Link Software and Documentation package (incl. J-Link USB driver) installed

J-Link connection

First, verify that the connection between the J-Link and PC is functional and J-Link Commander can communicate with the J-Link successfully.

• Connect J-Link via USB to the PC

Application running on the target

The general target functionality and correct has been already verified and is functional but after programming an application, J-Link is no longer able to connect to the device.

Issue: After downloading an application, J-Link is not able to connect to the CPU

This can have different reasons:

• Application disables the debug interface
• Application re-configures debug pins
• Application enters some kind of low power mode
• etc....

Preventing connection errors:

• Delay of 1 second at the start of a debug session, so in any case J-Link can halt the CPU before executing the "bad code"