I have one thing to add. RA4 is open collector when used as an output. I
am sure one could debate about what is acceptable. But I usually tie it
to ground if I'm not using it and don't want to waste a resistor on it.

Cheerful regards,

Bob


Roger Weichert wrote:
> From: "Olin Lathrop" <olin_piclist@embedinc.com>
> 
>> Roger Weichert wrote:
>>> I'm building a project (using a PIC16F627) and have reached the stage
>>> where I'm ready to design the board layout, so need to decide what
>>> I'm going to do with the unused port lines. ...
>>>
>>> I'm aiming for a tiny pcb with no wasted space, so am trying to avoid
>>> any components I don't absolutely need to have.
>> In that case make them outputs and make sure the firmware drives them.
> 
> 
> So if I make sure (right at the start of my program) to put in the code
> to set the unused pins as outputs, there should be no conflict in leaving 
> them
> open and I should be able to forget about them from there.
> 
> 
>> If any are input-only pins, then tie them to Vss or Vdd directly or thru a
>> resistor.
> 
> 
> and same as above? As long as I address their function by setting them up in 
> my initialisation,
> they can happily survive regular resetting and restarting for whatever 
> reason ...
> without potentially causing problems down the track.
> 
> 
>> If you have a little extra space, bring the unused pins out to pads and
>> still make sure they are driven.  If you have a little more extra space 
>> you
>> can add 100Kohm pullup or pulldown resistor pads.  You don't actually have
>> to load the parts, so it's only a board area issue.  Any changes to make 
>> use
>> of the pins would require rework and firmware change anyway.  The parts 
>> can
>> be added to the pads and the firmware changed at that time to make pins
>> inputs if that's what's needed.
> 
> 
>  OK, I can understand the sense in doing this  ... in fact I probably can 
> afford to
> take the space on this board to do it. (probably cant afford NOT to)
> 
> Thanks for your input Olin, it has helped a lot.
> 
> Regards,    Roger
> 
> 
> 
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