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Electronic design for JTAG/SWD

Associate II

Hello everyone,
I've been looking for some time for an example of an electronic design that would allow me to use the STLINK-V3MINIE in JTAG mode.


With my electronic schematic I can use it in SWD mode, which works very well.
However, it's impossible to use JTAG mode, because when I configure the debugger in STM32CubeIDE and start debugging I get:
"Error in initializing ST-LINK device. Reason: Unknown MCU found on target."



I wonder if my electronic diagram is correct, even if I refer to the AN5474 documentation on page 26.


Could someone either correct my circuit diagram or explain how to make the JTAG work?


Thank you in advance.


PS: I Use an STM32F722RE MCU

ST Employee

Hello @Boris19 and welcome to the ST Community 😊.

I suggest you to refer to the part 5 of the AN4661 and specially the Figure 22. JTAG connector implementation which shows the connection between the STM32F7 Series and a standard JTAG connector. The one that you are using is for the STM32MP13 series.

Best Regards.


To give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.

Pavel A.
Evangelist III

Why to use JTAG mode at all with STM32 MCUs? Do you need to chain several targets?

Hello @STTwo-32 and thank you for the fastest response I've ever had :).
Indeed, it's better to use the right document.
That said, document AN4661 does not use the STDC14 connector, nor does it contradict my electronic assembly (chap. 5.3.4).


Furthermore, according to chapter 5.3.3, it would appear that the pull-up and pull-down resistors are internal.
The only thing is that my 100 ohm "GND_DETECT" resistor doesn't exist.


So why isn't it working?

Best Regards.

Hello @Pavel A. ans thanks for your reply.
You're absolutely right, and in my case it would seem to be much better to use SWD.
But still, how to make it work.
Why doesn't my schematic allow the use of JTAG?

Best Regards.