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Forum Index : Microcontroller and PC projects : Unused Pins..?
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Zonker Guru  Joined: 18/08/2012 Location: United StatesPosts: 761 |
Merry Christmas and Happy New Year All..!! Just got a quickie question... I am trying to tie up a few loose ends on a project design, and while hooking in the MPU, I found a few unused pins. Is it ok to just leave them floating, or should they be tied to the supply like the PDF MCU manual says..? I don't have many examples of others work, but it seems most just float the extras.. Are the extra pins not used for anything..? Anyway.. Nuf bable... Thanks for any feedback..!! 2013-12-27_224621_PIC32-64pin_pinout.pdf |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9308 |
I tend to opt for tying unused IO's to deck(GND) via 10k resistors. I choose deck, as tying some pins to supply(5v) will kill the PIC, as not all pins are 5v tolerant. All pins are, however, ground-tolerant. 
It's a matter of opinion, really. If the PIC datasheet says you should, then you probably should. In all my testing and development, I have left unused pins floating. In the final version, I will be ground-referencing any unused IO pin with the aforementioned 10k, just to be sure that there cannot be any instability. If you are not referencing unused IO's in your code, one would think that it should not matter, but in practise, un-referenced IO's can cause issues - I have indeed seen it, mostly in my own designs, which, when the unused IO's are tied to ground via 10k resistors, the problems vanish. This could be something with my design, naturally - I'm just saying, is all... Smoke makes things work. When the smoke gets out, it stops! |
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jman Guru Joined: 12/06/2011 Location: New ZealandPosts: 711 |
My two cents worth Why not set the unused pins to outputs and set them low? Regards Jman |
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| JohnS Guru Joined: 18/11/2011 Location: United KingdomPosts: 3804 |
Microchip say what to do in the data sheet. As I recall, output and low is what they say but I'd read the sheet :) Tied low can't do much harm can it? What you don't want are floating inputs. Especially not with CMOS as they'll tend to pick up charge and swing around if not cause lock ups. John |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9308 |
Yeah, that's probably preferable over my 10k idea, just as that can be done in the code, whereas fitting 10k resistors to all unused IO's..... Are the MM IO's inputs or outputs by default? Smoke makes things work. When the smoke gets out, it stops! |
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| Zonker Guru Joined: 18/08/2012 Location: United StatesPosts: 761 |
Sorry Guys... What I meant to say was the "undefined pins" not used by MM-Basic... They are the unconnected pins in the PDF file. Pin 4 - RG6, Pin 11 - RB5, Pin 14 - RB2, Pin 21 - RB8, Pin 33 - RF3, and Pin 46 - RD0... I haven't checked through the source code yet to see if anything is done to protect the pins by, (let's say) making them outputs.. I don't have a lot of example schematics, but I was looking at the Mini Maximite board as a guide. Looking at the schematic, these pins are not mentioned... I can't seem to find any schematics on the CGMMSTICK1 either... Anyway, I was wondering if anyone has created a board using the PIC32 - 64 pin part and what they did with these "unused" pins.. Again, Thanks for the feedback gent's..!! |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9308 |
I will go out on a limb here and speculate that those physical pins on the PIC32 chip itself are not an issue - otherwise the circuit for the MM would have included them, and the PCB's would also include some kind of termination for them. The fact that they don't/didn't, seems to suggest that it is not an issue in the MM application. Perhaps Geoff could comment on that? Smoke makes things work. When the smoke gets out, it stops! |
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