National Instruments PCI-8430 - Page 135

ConnectingTwo-WireDevices
TheNIRS-485hardwareisdesignedtoworkwitheithertwoorfour-wire
devices.Ifyouareusingatwo-wiredevice,refertothedevice
documentationforspecificwiringinstructions.
Ingeneral,half-duplexnetworksuseasingletwistedpairofwiresfor
communicationinbothdirections,soyoumustconnectboththe
transmitterandthereceiverateachendofthesamepairofwires.For
example,toconnectanRS-485dataacquisitiondevicetoaportonyour
boardusinghalf-duplexcommunication,youneedasingletwistedpairof
wires.Attheboard,connecttheTXD+andRXD+signals(pins8and4
onaDB-9connector,pins5and20onaDB-25connector)togetherand
toonewire.ConnecttheotherendofthiswiretoboththeTXD+and
RXD+signalsonthedataacquisitiondevice.Usethesamemethodto
connecttheTXD–andRXD–signals(pins9and5onaDB-9connector,
pins22and7onaDB-25connector)tothesecondwire.
Forinformationaboutsettingthetransceivermodefortwo-wire
communication,refertoRS-485TransceiverControl.Formore
informationaboutduplexarchitectures,refertoSerialPortInformation.