Owner's manual

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36!
Appendix"Z!RS485&Bus&1.;;+G,@.;"
! General!Property!of!RS485!Bus!
According!to!RS485!industry!bus!standard,!RS485!is!a!half?duplex!communication!bus!which!has!120Ω!characteristic!
impend en c e,!th e !maximum!load!ability !is!3 2 !p a ylo a d s!( in clu d in g !co n tro lle r!d e vic e !an d !c o n tro lle d !d ev ice ).!
! RS485!Bus!Transmission!Distance!
When!using!0.56mm!(24AWG)!twisted?pair!line,!according!to!different!baudrate,!the!maximum!trans m ission !distan ce!
theory!table!is!shown !as!belo w: !
Max.!Distance!of!RS485!Transmission"
R2A</2,+"
62Y"Q@>,2;G+"
2400BPS!
1800m!
4800BPS!
1200m!
9600BPS!
800m!
!
The!transmission!distance!will!be!decreased!if!we!use!the!thinner!cable,!or!use!this!product!under!the!strong!
electromagnetic!interference!situation,!or!there!are!lots!of!devices!are!added!to!the!bus;!on!the!contrary,!the!
transmission!distance!will!be!increased.!
! Connection!Methods!
RS485!industry!bus!standard!require!daisy?chain!connection!method!between!any!devices,!both!sides!have!to!
connect!a!120Ω!terminal!resistance!(show!as!Diagra m!1),!the!sim plif ied !c o n n ec tio n !method!is!sh o wn!as!diagra m!2,!
but!the!distance!of!“D”!should!not!be!too!long.!
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Figure!A?7!RS485!Connection!1!
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Figure!A?8!RS485!Connection!2!
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! Problems !in!the!Practical!Application!
Normally,!users!adopt!star?shape!connection!method!in!construction,!under!this!situation,!the!terminal!resistors!must!
be!connected!between!two!farthest!devices!(as!Figure!A?9,!1#!and!15#),!b u t!t h is !co nnection!method!i s!n o t !sa t is fy !th e !
requirement!o f!the!R S4 85 !indu stry !stand a rd!so !that!it!w ill!lead!to!so m e!p rob lems!such!as!signal!reflection ,!anti? ja mming!
ability!decline!when!the!devices!are!faraway.!At!this!time,!the!dome!will!be!uncontrollable,!or!self?running,!etc.!
120Ω
120Ω
1#
2#
3#
4#
32#
D
主控器
A+
B-
A+
B-
1#
2#
3#
31#
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