J-Link Not connecting to Target Board

    This site uses cookies. By continuing to browse this site, you are agreeing to our Cookie Policy.

    • J-Link Not connecting to Target Board

      I tried connecting the J-link EDU mini to my target board via SWD and it can seem to connect. The target board is a custom PCB which features the STM32F401RDT6 microcontroller. I connect the SWDIO and SWDCLK pins together, also the ground and VRef pin. This is what I get as the output :

      Output

      SEGGER J-Link Commander V7.94c (Compiled Jan 3 2024 15:17:49)
      DLL version V7.94c, compiled Jan 3 2024 15:17:37

      Connecting to J-Link via USB...O.K.
      Firmware: J-Link EDU Mini V1 compiled Dec 13 2023 14:36:33
      Hardware version: V1.00
      J-Link uptime (since boot): 0d 00h 05m 24s
      S/N: 801043014
      License(s): FlashBP, GDB
      USB speed mode: Full speed (12 MBit/s)
      VTref=3.265V


      Type "connect" to establish a target connection, '?' for help
      J-Link>connect
      Please specify device / core. <Default>: STM32F401RD
      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 "STM32F401RD" selected.


      Connecting to target via SWD
      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.
      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 209ms
      Cannot connect to target.


      Any help would be greatly appreciated.

    • Hi,
      A good way to approach such an issue is usually the following troubleshooting guide:
      wiki.segger.com/J-Link_cannot_…the_CPU#Target_connection

      Additional hints:
      1) The STM32F4 devices allow to set permanent protection (RDP level 2),
      which will effectively disable the debug features of the chip.
      So if RDP level 2 is set, you will never be able to connect to the chip.
      2) In some cases, applications do override the debug pins.
      In such a case you would also have to connect the nRESET pin between J-Link & Device.
      Otherwise the connect under reset can not work, which is basically the only way to connect to the device in such a case.

      BR
      Fabian
      Please read the forum rules before posting.

      Keep in mind, this is *not* a support forum.
      Our engineers will try to answer your questions between their projects if possible but this can be delayed by longer periods of time.
      Should you be entitled to support you can contact us via our support system: segger.com/ticket/
      Or you can contact us via e-mail.

    • Hello,

      I tried your second suggestion and it didn't work. I used a multimeter to check the voltage of the SWDIO and SWDCLK signals, I get 0.16V and 0.5V respectively. Does this tell you something?

      The post was edited 2 times, last by John1234 ().