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Date of registration: Oct 29th 2017

Posts: 1


Friday, December 1st 2017, 4:44am

Identify a non standard JTAG interface

I have a couple old devices running NXP iMx251 or ARM926EJ-S processors. It looked like they had a JTAG connector in the same pin configuration as the j-link mini so I figured I'd start with that. But when I connect, the message I get is "Cannot connect to target" Can the j-link mini detect which pins are TDO, TDI etc? If not, any suggestions on how to start figuring it out? I'm tried working on them with a multi-meter, but I've only been able to find reset and ground.


Super Moderator

Date of registration: Jan 2nd 2017

Posts: 430


Friday, December 1st 2017, 9:13am


Thank you for your inquiry.
Generally you should be able to at least connect to iMX25 processors and some ARM926EJ cores.
A full list of all currently supported devices can be found here:

Can you post a screenshots of the J-Link Commander like described here when connecting?
To find out which pins are which it is the easiest if you have the schematics of the boards you want to use.
Are they eval boards or custom hardware?
If eval, which exactly?

For JTAG tag the pins need to be wired as follows for the J-Link to detect them:…ce-description/

Should you not have the schematics you will most likely need to use a Oszilloscope to resolve the signal change on TDO/TDI.
To use a Multimeter you can force signals on the J-Link side high or low with the Scriptfile function JLINK_PIN_Override() described in the J-Link User Manual.

Best regards,