Microgate SyncLink GT2 - Differential Fail-Safe Biasing

DifferentialFail SafeBiasing
Fail‐safebiasingisatechniquethat guaranteesdifferentialinputsi gnals areinasteadystatewhennot
connectedtoanactivedifferentialoutput.Optionalfail‐safebiasingofalldifferentialinputs(RS‐422/RS‐
485/V.11)foraportisavailablebyinstallingaresistorpackinthesocketlabeled‘FAILSAFE’.Thisresistor
packisnotincludedbydefaultwiththehardware.ContactMicroGatesalestorequestfail‐saferesistor
packswhenorderingthehardware.
Fail‐safebiasingisonlyusedwhenaninputisnotconstantlydrivenbyanoutput,andthatinputis
terminated(seeprevioussectionondifferentialinputtermination).Whenaninputisnotterminated,
fail‐safebiasingintegraltoeachreceivercircuitmaintainstheinputinasteadystate.Whenaninputis
terminated,externalfail‐safebiasing(resistorpack)mayberequiredtoguaranteetheinputisina
steadystate.
Anexampleapplication thatusesfail‐safebiasingis busmodeconnect ionswhereasinglecable
conductorpairisconnectedtoboththetransmitdataoutputandreceivedatainputformorethanone
station.Inthissetup,onlyoneoutputmaybeactiveatthesametimeandeachoutputisonly driven
whensendingdata.Whennostationissending,theexternalfail‐safebiasingmaintainsavoltageonthe
cablepairthatkeepsinputsinasteadystate.
WARNING:Fail‐safebiasingmustbepresentononly asinglestationconnectedtoacablepair.This
singlestationmaintainsthevoltageonthecabletokeepallconnectedinputsinasteadystate.Applying
fail‐safebiasingatmultiplepointsonacablemayres ultinincorrectoperation.
Figure4 FailSafeBiasingSockets
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