User manual

TheRs485Busstandardsrequireadaisy-chain
connectionbetweentheequipment.Theremustbe
terminationresistorswith120(asthepicture10-
4.1).Pleaserefertopicture10-4.2forsimple
connection.Dshouldnotexceed7m.
Ø Connectionandterminationresistor
Ω
10.4Rs485Busbasicknowledge
120Ω
1#2#3#4#32#
Picture10-4.1
120Ω
120Ω
1#2#3#4#32#
D
A+
B-
A+
B-
Picture10-4.2
120Ω
2400BPS
4800BPS
9600BPS
1800m
1200m
800m
Baudrate
Maxdistance
19200BPS 600m
Ø
Theterminationresistorisreadyontheprotocol
PCB.Thearetwokindsofconnection(asshow10-4.3
form).Itisthefactorydefaultconnection.Thejumper
capofswitchboardisseatedonpin2&Pin3andthe
terminationresistor120isnotconnected.
Whenconnectingthe120terminationresistor,
usershouldpullouttheprotocolPCBandplugthe
jumperonPin1&pin2.InstallthePCBbackandthe
terminationresistorisconnected.
(asshowthepicture10-4.3)
Theconnectionof120teminationresistor:Ω
Ω
Ω
Factorydefaultsetting
Connectionof120setting Ω
1 2 3
On
On Off
Onmeansinsertthejumpercap
Off
On
On
Picture10-4.3
AsspecifiedbyRs485standard,Rs485Busis
ofhalf-duplexeddatatransmissioncableswith
characteristicimpedanceas120.Themaximum
loadcapacityis32unitloads(includingmain
controllerandcontrollerequipment)
Ω
Ø CharacteristicsofRs485Bus
Ø
TransmissiondistancesofRs485Bus
Whenuserselectsthe0.56mm(24AWG)twisted
pairwiresasdatatransmissioncable,themaximum
theoreticaltransmittingdistanceareasfollow:
Ifuserselectsthinnercables,orinstallsthe
domeinanenvironmentwithstrongelectromagnetic
interference,orconnectslotsofequipmenttothe
Rs485Bus,themaximumtransmittingdistancewill
bedecreased.Toincreasethemaximumtransmitting
distance,dothecontrary.
38
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