cancel
Showing results for 
Search instead for 
Did you mean: 

Reset pin - add external pullup, or not?

bsuthar
Associate II

Hello team,

Generally , Reset pin by default status is Logic High.

But in AN4206 ( Page 31) , NRST pin is not Connected to 3.3V , it is left Floating with Capacitor.

Is that Okay ? 

My device is STM32F303.

Regards,

8 REPLIES 8
TDK
Super User

Yes, the typical connection is floating with 0.1 uF cap. It is internally pulled up.

TDK_0-1754142734193.png

 

If you feel a post has answered your question, please click "Accept as Solution".

Thank you , TDK

Would it Enable By Default or any Configuration Needed ?

Would it be Good Idea to pull-up NRST pin Externally as well ?

 

Regards,

HenrikGlader
Associate II

I think you're good to go.

Optionally, if you don't need to bring the internal reset out, you can make this pin GPIO.

Check the "FLASH_OPTR" register.

Though I dare not say if the internal reset state is fully reliable.

We have an external pull-up, just to be safe.

Hi Henrik,

One concern with ext.pull up is , it may paralle with internal pull-up to reduce resistance.  In my case , ext pull up will be 10k. We want to keep Reset function for USB DFU Bootloader.

Regards,

Bhupendra

 

No configuration needed.

Pulling it high externally does not add any functionality. It is unnecessary.

If you feel a post has answered your question, please click "Accept as Solution".

I would use an external pull-up for EMC reasons, if the reset line is connected to other IC's on the board. (The PCB track is like an Antenna for EMC, and can generate an unwanted reset).

The 0.1 uF cap protects from parasitic resets, not the pullup.

If you feel a post has answered your question, please click "Accept as Solution".

True, but not entirely if the EMC signal is amplitude modulated (as a lot of Standard test's require).