Differential is the way to go, and ideally not DC coupled to your ground.=20
I infer that you are powering node(s?) through the +12V and ground.  Ground=
 is a long resistor, and the nodes will be dumping various amounts of curre=
nt into it.
So, low over there is likely to be significantly higher or lower than low o=
ver here.  Same for high.



--=20
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