Unused Pins on BS2P-24- What to do with them???

DChap

What is the best practice for terminating unused I/O pins on the Bs2P?

Tie them all together and pull them UP using a 10K?
Tie them all together and pull them DOWN using a 10K

Or tie them up / down individually using a 10K?

I have a stamp project where I am not using Pins 4 - 15. Just want to follow best practices.

Thanks

Don

Post Edited (DChap) : 2/10/2005 9:09:39 PM GMT

Paul Baker

http://forums.parallax.com/showthread.php?p=525439

this applies to stamps as well. Safest is to use individual resistors, use a SIP bus resistor pack.

Beau Schwabe

Make them all outputs in software... that way they won't "float" and cause any unnecessary current drain.

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Beau Schwabe - Mask Designer III

National Semiconductor Corporation
(Communication Interface Division)
500 Pinnacle Court, Suite 525
Mail Stop GA1
Norcross,GA 30071

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Paul Baker

Output works, but there is a slim chance you get a super-goofy code execution caused by some unanticipated chain of events resulting in setting the unused pins back to input. Granted the likelyhood of it happening is extremely small but its not zero.

DChap

Thanks,

Good info in the link.

I will make them all outputs in software and tie them High.

BUT, can I tie all the pins together and route them all to +5v through 1 Pull Up resistor? I am out of space on my board.

Beau Schwabe

DChap,

If it were me I would do one or the other but not both... Either tie all inputs HIGH (or LOW)

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OR

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make all UNUSED pins outputs in software

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Beau Schwabe - Mask Designer III

National Semiconductor Corporation
(Communication Interface Division)
500 Pinnacle Court, Suite 525
Mail Stop GA1
Norcross,GA 30071

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DChap

Thanks Beau,

Making them Outputs in software is easy enough - done deal - and like I said, I don't have any real estate left on the board for Pull Ups..

Thanks again..

Don

Paul Baker

Its generally not advisable to use a single pullup/pull down resistor, 99.999% percent of the time (exact number of 9's is unknowable) there wouldn't be any problem (when they are set to input). If if that freak occurance happens where your port direction is switched (in this instance from input to output) and one is trying to drive it high and another is trying to drive it low, very bad things can happen (this creates a low impedance path from your power supply to ground) and would fry your stamp and possibly cause a fire. If you truely don't have the room, configure them as output and don't connect them to anything. If the freak occurance happens, you'll get unessesary current draw caused by the floating pins but you won't fry your stamp.

Post Edited (Paul Baker) : 2/10/2005 9:43:50 PM GMT