Hi, I had the same discussion on another board = but for CAN bus. = I = was also convinced that the 3rd wire is needed but it appears that some = driver/receiver chips have very high common mode input range which helps fo= r = the 2 wire solution. See the INA117 for example - = . +/-200V common mode range = but = I think this is extreme. Anyway, there where some app notes for CAN bus driver and receiver chips th= at = discussed this, but of course I can't find them now. /Ruben > We had a discussion on a Dutch forum about profibus (the RS485-based > version) being 2 or 3 wires, that is: does it need a > ground/reference/earth wire or not. I was convinced that it needs the 3d > wire, but reading some documentation leaves me in doubt. > = > Does anyone know the definitive answer? Can profibus couple devices > without a 3d wire (either in the cable or implicit in the grounding of > the various nodes)? If so, how does it cope with ground potential > differences in relation to the input range of the receiver chips? > = > Wouter van Ooijen > = > -- ------------------------------------------- > Van Ooijen Technische Informatica: www.voti.nl > consultancy, development, PICmicro products > docent Hogeschool van Utrecht: www.voti.nl/hvu > = > = > = > -- = > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > = =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D Ruben J=F6nsson AB Liros Electronic Box 9124, 200 39 Malm=F6, Sweden TEL INT +46 40142078 FAX INT +46 40947388 ruben@pp.sbbs.se =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist