STM32F746ZGT6 problem with custom board [urgent]

[aksulumdeniz]

Posted on July 04, 2017 at 21:00

Dear all,

   We have been developing a custom board featuring STM32F746ZGT6, and we have encountered some problems.

   We are able to program the MCU using the ST-link with no problems, however, the MCU does not do anything! The PCB design was exactly based on the NUCLEO-STM32F746ZG board. We could not spot any differences between the NUCLEO board and our custom designed board (for the essential MCU components).  

   At first, we thought that it was a software problem so we tried the same software with the NUCLEO board and it worked fine. All the clock sources etc. are identical in both the NUCLEO and our custom board. Therefore we suspect that there is a problem with the hardware. It could perhaps be due to EMI?

   We have double checked all the connections and soldering.

   We are in a desperate situation. Do you have any ideas what could be the source of such a problem? 

All help would be appreciated. Please let me know if you need any more information.

All the best,

Mehmet Deniz Aksulu

#stm32f7 #no-response-from-the-target #custom-board

[Andrei Chichak]

Posted on July 04, 2017 at 21:25

Is your crystal ringing?

[aksulumdeniz]

Posted on July 04, 2017 at 21:28

No. There is only a slight voltage offset. I can send you the oscilloscope images tomorrow.

We soldered the same crystal and capacitors to the NUCLEO board and uploaded the same software. The oscillator is ringing there... 

[Andrei Chichak]

Posted on July 04, 2017 at 21:35

Don't bother. What you want to do is start a project in CubeMX that does very little. Set up the clock chain the way you would expect, but turn on MCO1 and MCO2 to show you what the various clocks are doing.

Try using the internal high speed clock and make sure you can see something correctly on pins 99 and 100. If that works, flip over to your external crystal.

Unless you can get your clock stable, you're going nowhere.

Andrei

[Andrei Chichak]

Posted on July 04, 2017 at 21:36

Also, a slight voltage offset sounds like your board needs cleaning. Pour on some isopropanol and scrub it with a toothbrush.

Andrei

[aksulumdeniz]

Posted on July 04, 2017 at 21:38

Will do! I will try that tomorrow and will keep this post updated.

Thanks a lot for your response.

[aksulumdeniz]

Posted on July 04, 2017 at 21:38

OK

[aksulumdeniz]

Posted on July 05, 2017 at 14:15

Dear Andrei,

I have created a CubeMX project with only the internal oscillator.

The code works fine on the NUCLEO board. I can see the clock signal from pins 99 and 100.

However, when I upload the same code on our custom board there is no signal. All pins are slightly above ground level.

What do you think could be the problem? It is for sure due to hardware.

All the best,

Mehmet Deniz Aksulu

[Tesla DeLorean]

Posted on July 05, 2017 at 14:50

But presumably you are successfully loading code via SWD, if you step into it with a debugger, what are you learning about the code execution, and if/where it might be stuck?

BOOTx pins?

Voltages at VCAP pins?

State of NRST?

[aksulumdeniz]

Posted on July 05, 2017 at 14:59

We have not tried to debug the MCU yet. When I do I will inform you.

NRST is at 3.3 V (high).

The VCAP's are at about 1.35 V.

BOOT0 pin is pulled down to GND. There is no BOOT1 for STM32F746ZGT6.