Howdy,

some (ds)PICs with big memory come only with a high number of pins. So,
if I only need to use few I/Os, one thing I usually do is to leave the
unnecessary ones unconnected, and then (immediately at reset time, and
if I'm being paranoid about cosmic rays, every now and then in the main
loop or in some interrupt routine) the first thing I do is to set those
PORTs as output to avoid (as you may have already well intuited) floating
inputs, which draw unnecessary current, and probably do no good to the
transitors inside the chip as well.
Some people prefer to keep them inputs, and use resistors to tie them to
ground. I don't, because I don't want to solder unnecessary resistors and
because the PCB is much simpler (and allows more opportunities to route
other signals) if I keep those I/Os unconnected.

Anyway, now I am faced with this problem: my circuit must draw as little
current as possible (usually it sleeps), and there are some pins which
can be used as outputs, inputs, or tri-stated.
When they're outputs, no problems. When they're inputs, no problems
either (the other end will make sure the line is not floating), but when
they must be tri-stated, then I'm faced with a problem.

The best solution I thought so far (and I am writing to seek a possibly
better option I'm currently ignoring) is a 1M resistor to ground (not
Vdd, but ground. It seems there's less leakage current this way, but it
may be only the case I measured).
10Mohm was definitely too much, and 100K (or so) will draw unnecessary
current, so I've selected the magic 1M value.

Do you think there's a better approach to the problem?

Thanks,
Mario

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