PCB design layout

Discussion in 'The Projects Forum' started by arslankhan, Feb 26, 2013.

  1. arslankhan

    Thread Starter New Member

    Jan 23, 2013
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    Hi to all,
    I am new here i have desinged a UHF pcb desing. I am working on atmmega128 rf1. i want to know about the pins of microprocessor that are not used .should we ground them???.
    Kindly guide me about that.
    thanks,
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,449
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    Leave unused pins not connected but configure them as output.
     
    arslankhan likes this.
  3. JMac3108

    Active Member

    Aug 16, 2010
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    66
    I like to connect all the unused pins to test points (just a SMD pad or thru-hole) on the PCB. This makes it easy to wire to them later if (when) you find a problem or the sytem requirements change and you need to modify it.
     
    arslankhan likes this.
  4. MrChips

    Moderator

    Oct 2, 2009
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    Excellent suggestion. I do this too.
     
  5. arslankhan

    Thread Starter New Member

    Jan 23, 2013
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    Thnaks @JMac3108 and @MrChips ...It is written in datasheet that we should add pull up resistors with unused pins avoiding floating value for power consumption
     
  6. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    Don't they also have WPU (weak pullup) like PICs?

    Normally I ignore unused I/O, setting it to output of course allows you to leave it open in any case.

    I also often see it on PCBs- some controller pins not connected at all. Never really saw a ring to connect them all or resistor networks even.

    An unconnected output should not draw any serious current, consult your datasheet about that (Electrical specifications).
     
  7. JMac3108

    Active Member

    Aug 16, 2010
    349
    66
    Yes, you can add pull-ups and set the pins to inputs. Or you can set the pins to outputs without the pull-ups. You want to avoid floating inputs.
     
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