Olin Lathrop wrote: >> To be "safe", it is best to tie unused input pins to ground [or Vcc, >> doesn't much matter which] *ONLY* through a resistor, rather than >> directly with a short. This is not superstition, as during code >> development it is all too easy to accidentally configure a pin >> intended as input to output. You then run the risk of >> short-circuiting an output. > >Perhaps in a low volume product. I wouldn't want to burden a high volume >product with unnecessary parts for a minor debugging convenience. > Even in a high volume product, personally I would never simply (a) configure a pin as output and then leave it unterminated, or (b) set a pin to input and then short straight it to gnd. There are a number of possible "disastrous" scenarios this way: 1 - with (a), an ESD spike might modify the TRIS register, set an output pin to input, and then it would float and pick up noise, and possibly affect proper operation. 2 - with (b), an ESD spike might modify the TRIS resgister, set an input pin to output, and fry your product. 3 - with (b), on the next go round with code development, you might do the TRIS thing yourself by mistake. 4 - with (b), it takes more work if you want to use the pin differently in the future. 5 - other circumstances may accidentally mod the TRIS register in the field, eg brownouts, lightning crashes, screwy things related to general susceptibility of the /MCLR pin, who knows what. Better to spend a few pennies and tie the unused pins to gnd via a bussed SIP resistor net, and improve the reliability of your product. Also, as mentioned several times, it helps saves the butt of those of us in the subset of non-perfect coders when they screw up during development. Good practice for code dev, good practice for field reliability. In a nice "guaranteed" noise-free field environment, you might be ok doing it the "quick-and-dirty" way. But, all in all, better safe than sorry. Experience, yes. Superstition, no. - danM -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.