Applying 0 V to DEC2 causes freeze which cannot be returned using RESET pin.

[Haruki Kawakami]

Hi,

Once applying 0V to DEC2 pin, CPU hangs up and cannot be system resetted even though we input reset signal to RESET pin. 

The only way to reset is to suppress system voltage supply and resume it. 

How can we return from such a freeze without suppress/resume system voltage supply?

Regards,

[run_ar]

Hi,

Why do you connect dec2 to 0v? The product specification says this should not be connected see reference schematic.

Best regards,

[Haruki Kawakami]

Hi,

Of course DEC2 is not connected to ground on our board, but sometimes static electricity connects DEC2 to ground.

[run_ar]

Hi again

That does not make sense. How does that happen? Please note that the chip is tested for ESD, In the datasheet you can see that the maximum values for a limited amount of time are:

ESD HBM	Human Body Model		4	kV
ESD CDMQF	Charged Device Model (AQFN73, 7×7 mm package)		750	V

Exceeding this limits might damage the chip.

[Haruki Kawakami]

Hi

This is an actual problem. We carried out ESD test to our product, then CPU hung up, and sending reset signal to RESET pin or sending reset command via SWD had no effect. We analyzed what caused this symptom, and found that dropping DEC2 to ground for a moment caused the same symptom, so we assumed static electricity made DEC2 connected to ground for a moment.

Anyway, how this symptom happens is not important.

It is important to know how we can reset the CPU when such like this symptom happens. As I wrote above, sending reset signal to RESET pin or sending reset command via SWD had no effect.

Do you have any idea?

[run_ar]

Hi,

We only guarantee that the chip will not be damaged as long as the ESD is within the limits given above. Unfortunately we cannot control the state of the chip when this happens, so undefined behavior is expected. I am afraid the only way you can recover from this is by toggling power. I am sorry for the inconvenience. However, as said, it is not possible to predict the state of the chip after an ESD discharge.

[Haruki Kawakami]

Hi,

Thank you for describing. I understand I can recover from this is only by toggling power.