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I've got a device with STM32F439 microcontroller on it. I flashed the firmware using the J-Flash utitilty (flashed and read back data is same). Then started the application from J-flash: everyting works fine. But when I restart the application without connected J-link the device is not booting.

P.S.: I think it should work if I would perform hardware reset, but device should start automatically on power on.

Update #1: I found a test board with STM32F417 on it and repeated the same action. The same result. Not starting without connected J-Link. But when I push "reset" button - it starts immediately. May be I should perform some internal resets before start?

Update #2: controller boots when there is permanent high voltage level on NRST pin.

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    \$\begingroup\$ Unconnected grounds, perhaps? Seriously, without more details, we are useless. \$\endgroup\$ – Dzarda Jun 19 '14 at 14:28
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    \$\begingroup\$ Never used one with an STM32 but on some devices a J-Link will power the target by default, it could be as simple as you don't have power to the microcontroller when removed. \$\endgroup\$ – PeterJ Jun 19 '14 at 14:37
  • \$\begingroup\$ I'm agree with @Dzarda you have to put more details here. two pictures of two situations of your circuits will help too much. \$\endgroup\$ – Roh Jun 19 '14 at 17:25
  • \$\begingroup\$ Microcontroller has power without connected J-Link. \$\endgroup\$ – zenio Jun 20 '14 at 5:00
  • \$\begingroup\$ Check your initialization. Debuggers often do some initialization independently, which may be missing in the code. \$\endgroup\$ – starblue Jun 20 '14 at 7:35
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Found solution. The problem was in JTAG connector: he gave a low level on NRST pin so external reset occured indefinitely.

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