Tracks on PCB:s ar also transmission lines.
i.e if you have a PIC that drives one line leading to another PIC 20cm away on the other end oc a PCB, then that signal will overshoot, and it wil do it with what the transmitting PIC will drive into the line, transiently much more then the continuously allowed 20/25mA.

So the recieving PIC will recieve a transient of more than +-20mA overshoot current.

The theoretical model uses is driving Vdd/Vcc into a transmission line with recieving end Hi Z, but clamped to Vdd & Vcc.  The clamping vill recieve as much ctrrent as the driver some pioseconds earlier was driving into the line, for the PIC this is transiently much more tna 20/25 mA)

So, basically, PICs are incompetent of recieving signals from each other without additional protection?  (such as at least line driving series resistors)

/Morgan
Morgans Reglerteknik, HŠllekŒs, 277 35 KIVIK, SWEDEN
   tel +46(0)414-446620, fax -70331,   mrt@iname.com