STM32 Virtual COM Port and BREAK

[T B]

Posted on January 29, 2018 at 12:02

Hello!

Is it possible to send a UART break (0.3 seconds) over the Virtual COM Port.

It seems that UART break is connected with NRST.

-Thomas

[Andrew Neil]

Posted on January 29, 2018 at 12:28

Is it possible to send a UART break (0.3 seconds) over the Virtual COM Port

In which direction?

• PC --> STM32?
• STM32 --> PC?

[T B]

Posted on January 29, 2018 at 13:45

PC --> STM32 (The STM32 resets.)

On the PC I generate the break with RealTerm or with pyserial. Both has the same effect.

[Andrew Neil]

Posted on January 29, 2018 at 14:12

Now I'm confused.

So you're saying that you are sending a break, and that it causes your STM32 to reset?

But you don't want the STM32 to reset?

So why not use the debugger to see what happens when you send that break ... ?

[Bogdan Golab]

Posted on January 29, 2018 at 14:27

Are you running a custom application on the STM32 or you are in the DFU mode (bootloader)?

[T B]

Posted on January 29, 2018 at 14:56

I have tried it on the STM32F3DISCOVERY and NUCLEO-F302R8 boards. Both have the same behavior.

If I press ''Set Break'' in RealTerm'' then PIN T_NRST (PB0) of the ST-LINK MCU (U2) assert low and

the MCU (STM32F30X) resets.

[Bogdan Golab]

Posted on January 29, 2018 at 15:05

Ok. It means that the st-link captures the ctr-c and resets the target MCU.

STM32F3DISCOVERY does not emulates the VCOM because of st-link v2 so the VCOM should not be seen in the Device Manager, I guess

NUCLEO-F302R8has the VCOM (st-link v2-1).

It does not explain the behavior.

[Andrew Neil]

Posted on January 29, 2018 at 15:14

Note that a break is not the same as a Ctrl+C ...

[Andrew Neil]

Posted on January 29, 2018 at 15:15

Well, that's a whole load of information & context that was missing from the OP!

[Bogdan Golab]

Posted on January 29, 2018 at 15:54

Right. Thanks.