Alessandro: If this Ascii schematic is what you are describing:
port1--------+--------probe
port2--/\/\/\--|


then this pseudocode will do what you are describing:

set port1 input
set port2 input
 if port1=high, node=high
 if port2=low, node=low
now set port2 to output
 set port2=1. temp=port1
 set port2=0. temp2=port1
 if (temp=1) and (temp2=0) then node=high-z

Brian
-----Original Message-----
From: Alessandro Zummo <azummo@ITA.FLASHNET.IT>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Monday, January 26, 1998 9:22 AM
Subject: Logic Probe


> Probably most piclisters knows the Morgan Logic Probe..
> is based on a PIC 12C508 and is able to sense
> hree-states: 0,1, and high-z...
>
> The probe is simply connected to one pin and,
> trough a 100k resistor, to another pin....
>
> How does it works? i.e. how the third state
> is interpreted?