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What to do with unused microcontrolle...

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2005-2006 » Archive through 08 July, 2005 » What to do with unused microcontroller pins? « Previous Next »

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Jon_nic
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Username: Jon_nic

Post Number: 19
Registered: 05-2005

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Posted on Monday, 04 July, 2005 - 12:32 pm:   Edit Post Delete Post Print Post

if a microcontroller has unused pins that are floating, does this cause increased current consumption. what is the best method:- to tie them to ground and set them as inputs or outputs... or to tie them to +v?
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Mikehibbett
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Username: Mikehibbett

Post Number: 85
Registered: 04-2005

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Posted on Monday, 04 July, 2005 - 01:33 pm:   Edit Post Delete Post Print Post

yes. Also, there is an increased risk of ESD susceptibility.

Personally I leave them as unconnected programmed outputs. That way you can use them later for debug signals. IMHO the best solution is have them left as inputs and pulled low or high by a 1K resistor. Connecting directly to ground or supply is not a great idea since under noise conditions it is possible for I/O pins to change spuriously from inputs to outputs. Not likely but I have seen it happen.

Regards,

Mike.
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Adam
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Username: Adam

Post Number: 17
Registered: 06-2005

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Posted on Monday, 04 July, 2005 - 08:08 pm:   Edit Post Delete Post Print Post

Hi Jon
I would set them as outputs and set them high. You get a higher level of immunity if they are set high, it's harder for noise to pull lines low than spike them high.
That's why alot dedicated pin on IC's are active low, like resets.
Regards
Adam

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