) ▁and ▁ 0 ▁( on ), ▁by ▁the ▁polar ity ▁between ▁A ▁and ▁B ▁terminal s . ▁If ▁A ▁is ▁negative ▁with ▁respect ▁to ▁B , ▁the ▁state ▁is ▁binary ▁ 1 . ▁The ▁revers ed ▁polar ity ▁( A   + , ▁B   − ) ▁is ▁binary ▁ 0 . ▁The ▁standard ▁does ▁not ▁assign ▁any ▁logic ▁function ▁to ▁the ▁two ▁states . ▁ ▁Master - s lave ▁arrangement ▁ ▁O ften ▁in ▁a ▁master - s lave ▁arrangement , ▁when ▁one ▁device , ▁the ▁master , ▁initi ates ▁all ▁communication ▁activity , ▁the ▁master ▁device ▁itself ▁provides ▁the ▁bias . ▁ ▁In ▁this ▁configuration , ▁the ▁master ▁device ▁is ▁typically ▁cent r ally ▁located ▁along ▁the ▁set ▁of ▁R S - 4 8 5 ▁w ires , ▁with ▁two ▁slave ▁devices ▁located ▁at ▁the ▁physical ▁ends ▁of ▁the ▁w ires ▁providing ▁term ination . ▁ ▁Full ▁du plex ▁operation ▁ ▁R S - 4 8 5 , ▁like ▁R S - 4 2 2 , ▁can ▁be ▁made ▁full - du plex ▁by ▁using ▁four ▁w ires . ▁Since ▁R S - 4 8 5 ▁is ▁a ▁multi - point ▁specification , ▁however , ▁this ▁is ▁not ▁necessary ▁or ▁des irable ▁in ▁many ▁cases . ▁R S - 4 8 5 ▁and ▁R S - 4 2 2 ▁can ▁inter oper ate ▁with ▁certain ▁restrictions . ▁ ▁Con ver ters , ▁repe aters ▁and ▁star ▁topology ▁ ▁Con ver ters ▁between ▁R S - 4 8 5 ▁and ▁R