Tell me more ×
Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It's 100% free, no registration required.
up vote 3 down vote favorite
1

I have a question about ESD effect on MCU pins that troubles me. MCU pins configured as input, that are not pulled low or high are likely to make trouble, and very likely to make trouble in case of an ESD pulse.

But what about:

  • MCU pins configured as tri-state?
  • MCU pins configured as output?
  • Would it make a design more robust to configure unused MCU pins as output?
share|improve this question

1 Answer

up vote 6 down vote accepted
  1. Pins configured as "tri-state" are inputs.
  2. Pins that are actively driven high or low are at a low impedance, which makes them less susceptible to ESD. Outputs driven low are one case of that, so yes, that is a good thing to do with unused pins.
share|improve this answer
Every Pic datasheet I have ever read recommends driving unused pins low for this reason, and I believe that is generally the restart state of the TRIS and PORT registers. – CMP Apr 5 '12 at 18:54
@CMP The restart state of the TRISx registers is as input. – m.Alin Apr 5 '12 at 19:42
Interesting. Any insights to why, when they also recommend driving them low if unused? – CMP Apr 5 '12 at 20:33
@CMP Check out the answers to this question for some insight – m.Alin Apr 5 '12 at 21:56
@CMP: It makes sense for the pins to wake up in the most benign configuration for any external circuit. That is high impedance and to tolerate being driven to arbitrary voltages within the legal range. They can't know what pins you consider unused. Only you know how you're using the pins, so it's your job to set them up appropriately. That includes doing reasonable things with unused pins, like making them outputs and driving them low. – Olin Lathrop Apr 5 '12 at 22:07
show 3 more comments

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.