National Instruments PCI-8430 - Page 147

RS-485
AsspecifiedintheEIA-485Standard,StandardforElectrical
CharacteristicsofGeneratorsandReceiversforUseinBalancedDigital
MultipointSystems,RS-485expandsontheRS-422standardby
increasingthenumberofdevicesyoucanusefrom10to32andby
workingwithhalf-duplexbusarchitectures.UnliketheRS-422standard,
RS-485addressestheissueofusingmultipletransmittersonthesame
line.RS-485definestheelectricalcharacteristicsnecessarytoensure
adequatesignalvoltagesundermaximumload,aswellasshort-circuit
protection.RS-485canalsowithstandmultipledriversdrivingconflicting
signalsatthesametime.