Unused Opened Drain


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  1. #1
    teverett's Avatar
    teverett Guest

    Default Unused Opened Drain

    Pic 16F767 - application does not use all the available pins. I have set the used pins to = 0 and tied them to ground using a 10K resistor.

    Question:
    Can I leave Port A.4 pin#6 (open drain) float?

    If not what is the correct way to deal with this pin?

  2. #2
    Join Date
    Jul 2003
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    Colorado Springs
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    Default

    Along with setting all the UNused pins to = 0, you need to set them to OUTPUT. Or, just use LOW on each pin.

    Then there's no need for the external 10k's.

    And, if you set PORTA.4 to output low, it isn't floating, so no prob.

    HTH,
    DT

  3. #3
    teverett's Avatar
    teverett Guest

    Default Finishing the project

    ... I had finished this project and wanted to be sure how to handle open pins. I have left unused pins open in the past. I read this article http://www.piclist.com/techref/logic/xtrapins.htm on the web and it was not clear about an open drains. His reference to adding a resistor must be over kill.

    I will pull out the 10K resistor since that will just help me with space on board.

    Thank you the answer.

  4. #4
    Join Date
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    What to do with unused pins is always a long and endless debate. Personnaly i set them as input and use external resistors OR i tie them to GND (or VSS) via 0 ohms jumper or not. YUP, i still use the old method. Same thing for CMOS or else IC. All input to somewhere.

    If the unit is not powered, the pin is not set as output so MAY act as a big antenna waiting for the next ESD... so MAY cause some problem one day or another. BUT if you consider the board layout + enclosure insulation it give you another point of view.

    It's up to you to make your own decision.
    Last edited by mister_e; - 11th November 2006 at 19:26.
    Steve

    It's not a bug, it's a random feature.
    There's no problem, only learning opportunities.

  5. #5
    teverett's Avatar
    teverett Guest

    Default 2nd method

    I already removed the 10K resistor - tied the unused pins directly to ground and submitted the schematic to http://www.expresspcb.com/ for prototyping.

    So I am in a wait and see position here. I am sure it will be fine .. but there is a problem it is good to know an alternative.

    Thanks,
    Terence

  6. #6
    teverett's Avatar
    teverett Guest

    Default Two more open pins ---

    Pins # 9 & #10 on the 16F767 - {9-OSC1/CLKIN & 10-OSC2/CLKOUT} Should they be grounded as well? I noticed that I grounded along with the other unused Pin. I am using INTRC_IO so I do not use these pins.

    If they do not need to be grounded can they be - will it hurt if they are?

    Terence

  7. #7
    Join Date
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    Default

    Unused remain unused... OSC i/o or not they're unused, same rules apply
    Steve

    It's not a bug, it's a random feature.
    There's no problem, only learning opportunities.

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