Connection Issues with STM32H747 MCU on Custom PCBs

[JonConesa]

Hello!

I just received some custom PCBs with the STM32H747BIT6 MCU, but I’m having trouble connecting to it. I’m using a J-Link V12 and initially tried to establish the connection with jlinkexe. It correctly detects the voltage, but when attempting to connect, I always get the following error:

 jlinkexe
SEGGER J-Link Commander V8.46 (Compiled Jun 26 2025 07:49:05)
DLL version V8.46, compiled Jun 26 2025 07:48:31

Connecting to J-Link via USB...O.K.
Firmware: J-Link V12 compiled Apr  1 2025 10:02:39
Hardware version: V12.00
J-Link uptime (since boot): 0d 00h 00m 44s
S/N: xxxxxxxxx
License(s): RDI, FlashBP, FlashDL, JFlash, GDB
USB speed mode: High speed (480 MBit/s)
VTref=3.335V


Type "connect" to establish a target connection, '?' for help
J-Link>connect
Please specify device / core. <Default>: STM32H747BG_M7
Type '?' for selection dialog
Device>
Please specify target interface:
  J) JTAG (Default)
  S) SWD
  T) cJTAG
TIF>S
Specify target interface speed [kHz]. <Default>: 4000 kHz
Speed>
Device "STM32H747BG_M7" selected.


Connecting to target via SWD
ConfigTargetSettings() start
ConfigTargetSettings() end - Took 190us
InitTarget() start
SWD selected. Executing JTAG -> SWD switching sequence.
Error: Failed to initialized DAP.
Can not attach to CPU. Trying connect under reset.
SWD selected. Executing JTAG -> SWD switching sequence.
Error: Failed to initialized DAP.
Connecting to CPU via connect under reset failed.
InitTarget() end - Took 309ms
Connect failed. Resetting via Reset pin and trying again.
ConfigTargetSettings() start
ConfigTargetSettings() end - Took 34us
InitTarget() start
SWD selected. Executing JTAG -> SWD switching sequence.
Error: Failed to initialized DAP.
Can not attach to CPU. Trying connect under reset.
SWD selected. Executing JTAG -> SWD switching sequence.
Error: Failed to initialized DAP.
Connecting to CPU via connect under reset failed.
InitTarget() end - Took 311ms
Error occurred: Could not connect to the target device.
For troubleshooting steps visit: https://kb.segger.com/J-Link_Troubleshooting

I also tried using STM32CubeProgrammer, but I couldn’t connect to the MCU either. However, this tool displays the following errors:

18:39:25 : STM32CubeProgrammer API v2.19.0 | MacOS-64Bits 
18:40:14 : UR connection mode is defined with the HWrst reset mode
18:40:40 : xxxxxxxxx
18:40:40 : Error: J-Link - Connection to target failed
18:40:40 : Error: Unable to get Access port number
18:40:40 : Voltage     : 3.34V
18:40:40 : Error: Database cannot be found. DatabasePath = /Applications/STMicroelectronics/STM32Cube/STM32CubeProgrammer/STM32CubeProgrammer.app/Contents/MacOs/bin/../Data_Base/STM32_Prog_DB_0xFFF.xml
18:40:41 : Error: flash loader cannot be loaded. FlashLoaderPath = /Applications/STMicroelectronics/STM32Cube/STM32CubeProgrammer/STM32CubeProgrammer.app/Contents/MacOs/bin/FlashLoader/0xFFF.stldr
18:40:41 : Error: Database cannot be found. DatabasePath = /Applications/STMicroelectronics/STM32Cube/STM32CubeProgrammer/STM32CubeProgrammer.app/Contents/MacOs/bin/../Data_Base/STM32_Prog_DB_0xFFF.xml

Do you know what might be causing this issue?

Find attached the schematics:

[MHoll.2]

Please show all the MCU pin's (for example were are SWDIO / SWDCLK or the SMPS pins connected?).

The Power connecton is not what I'm expecting from a device with SMPS Power supply on chip. Please refer to the Reference Manual (RM0399) Capter 7.4 for Power connection possibilities.

p.s.: R17..R21 are 0R only two of them can be mounted, can you please tell us the mounted Resistors.

[Andrew Neil]

---

@JonConesa wrote:

using a J-Link V12 and initially tried to establish the connection with jlinkexe.

---

For specific help with Segger tools & software, ask Segger:

https://forum.segger.com/

https://www.segger.com/support/technical-support/

They have this on resolving connection issues:

https://kb.segger.com/J-Link_cannot_connect_to_the_CPU

And from ST:

https://community.st.com/t5/stm32-mcus/how-to-solve-connection-errors-when-connecting-and-programming/tac-p/786977

https://community.st.com/t5/stm32-mcus/how-to-solve-debugger-connection-issues/ta-p/49693

As @MHoll.2 suggests, it does also depend upon working hardware; see also Application note AN4938, 
 Getting started with STM32H74xI/G and STM32H75xI/G MCU hardware development