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F2 - unused i/o

Question asked by FatTony on Jul 20, 2013
Latest reply on Jul 21, 2013 by FatTony
Hi,

 I am a little unclear as to what Section 5.6 of AN3320 is recommending for unused I/O pins.

For example is configuring a pin as output low, open drain, with internal pull down resistor and unconnected pin, materially worse than adding an external pull-down to ground? Should I use external pull-downs?

Could I connect directly to ground without a resistor or could that short during initial power up? Could I connect all pins to ground using just one resistor for the lot?

It would be nice if I had a reliable solution that would allow me to leave the pins unconnected for future bespoke customization of this small volume product.

What is confusing is the conflicting comments from various sources.

For example, see this comment, but the source it quotes by ST-One has since been removed:
hmm-> "In Run mode you can just leave all your unused I/O pins on your PCB not connected and thru software configure them as Push-pull with Data 0. 
This maintains a static level with zero consumption and finally is the best reliable mode for EMI and EMS." 
Qouted from STOne-32's post in the thread: http://www.st.com/mcu/forums-cat-6110-23.html

I've also seen this comment, though it's not for F2:

                                   
           
If you look in "\FWLib\examples\GPIO\IOToggle\main.c" (v2), there's this: 
           
            /* Configure all unused GPIO port pins in Analog Input mode 
            (floating input trigger OFF), this will reduce the power 
            consumption and increase the device immunity against EMI/EMC */ 
           

All help greatly appreciated!

Thanks










 

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