I know data lines may act as transmission lines after about 3 inches of
length (at least in some cases) where reflections etc may be a concern, but
I'm wondering about my own situation right now.

I am reading in human-speed (time frame of seconds, not microseconds,
between data changes) digital ports that are pulled high and active low, and
the input is via "remote" switches.  There are 8 port "wires" brought 3 feet
away from the PIC, along with a 3 foot ground wire to the system board, and
the switches route an input to ground one at a time, so overall there's 6
feet between any given input and ground, and it works fine, but I'm
wondering if it's technically valid to design something this way, just 6
feet of wire runing directly between a PIC input and ground...

When does the transmission line effect become an actual concern, what type
of data transfer, is it more of an outgoing than incoming thing, or more of
a high speed than a low speed issue?

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