Issue downloading the code on STM32H743 over JTAG interface

[bsn_14]

Hello Guys,
    We've our own board with STM32H743BIT6 mcu Integrated. We've tried to dump the code by using the external ST-LINK V3 Debugger with JTAG Interface. It works fine for first 3 - 4 times. But then after reaching the board for the 5th time we're getting the Err message as "Error: ST-link error (DEV_TARGET_HELD_UNDER_RESET)".
Tried Methods:
1. We've Pressed the reset button for 2-3 seconds after giving the connection request.
2. We had set the Mode as Under Reset and Hot Plug mode
3. We've tried with STM32CubeIde also, still not working.

Note:
JTAG NRST pin in ST-LINK V3 Debugger is held at Logic Low, without connection to the target. Is this ok?

Suggest us some Solutions to overcome this state!
If anyone has the ST-LINK V3 Schematics send us.

[Andrew Neil]

What tools are you using for programming - STM32CubeProgrammer? other?

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@bsn_14 wrote:

 our own board with STM32H743BIT6 mcu Integrated. .

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Please post the schematics

https://community.st.com/t5/community-guidelines/how-to-write-your-question-to-maximize-your-chances-to-find-a/ta-p/575228

[bsn_14]

For Programming STM32CubeIDE we're using. For downloading the program to the Board we're using STM32CubeProgrammer. We're using JTAG Connection.`

Schematics: Our NRST Schematic is attached Below.

[SofLit]

Hello,

We invite you to check first your HW. You can refer for example to STM32H743I-EVAL schematics / Power, debug & clock part:

TRST is connected to pin 3 and NRESET is connected to pin 15 of the JTAG connector. 

[bsn_14]

We are using 14 pin JTAG and not 20 pin JTAG. Can we get schematics for ST-Link V3 MB1441B board?

[SofLit]

Seeing this link https://www.st.com/en/development-tools/stlink-v3set.html#cad-resources

There is no schematics for ST-Link V3 MB1441B available which means it's not something will be shared. But you can inspire from STLINK-V3 schematics embedded on one of the NUCLEOs.

Example: https://www.st.com/resource/en/schematic_pack/mb1364-h753zi-c01_schematic.pdf

[bsn_14]

This is not helping to resolve our problem. So, can we atleast know whether the JTAG_NRST (JNRST) output coming from STLINK-V3 is in which configuration i.e., whether in open drain or push pull?