From: "Olin Lathrop" > 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 -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist