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Appendix
4
R S485
B us
C onnection
General
P roperty
o f
R S485
B us
!
According
t o
R S485
i ndustry
b us
s tandard,
R S485
i s
a
h alf-‐duplex
c ommunication
b us
w hich
h as
1 20Ω
c haracteristic
impendence,
t he
m aximum
l oad
a bility
i s
3 2
p ayloads
( including
c ontroller
d evice
a nd
c ontrolled
d evice).
!
RS485
B us
T ransmission
D istance
When
u sing
0 .56mm
( 24AWG)
t wisted-‐pair
l ine,
a ccording
t o
d ifferent
b audrate,
t he
m aximum
t ransmission
d istance
theory
t able
i s
s hown
a s
b elow:
The
t ransmission
d istance
w ill
b e
d ecreased
i f
w e
u se
t he
t hinner
c able,
o r
u se
t his
p roduct
u nder
t he
s trong
electromagnetic
i nterference
s ituation,
o r
t here
a re
l ots
o f
d evices
a re
a dded
t o
t he
b us;
o n
t he
c ontrary,
t he
transmission
d istance
w ill
b e
i ncreased.
Connection
M ethods
!
RS485
i ndustry
b us
s tandard
r equire
d aisy-‐chain
c onnection
m ethod
b etween
a ny
d evices,
b oth
s ides
h ave
t o
connect
a
1 20Ω
t erminal
r esistance
( show
a s
D iagram
1 ),
t he
s implified
c onnection
m ethod
i s
s hown
a s
d iagram
2 ,
but
t he
d istance
o f
" D"
s hould
n ot
b e
t oo
l ong.
120Ω
1#
A +
D
B -
Controller
主控器
Problems
i n
t he
P ractical
A pplication
!
Normally,
u sers
a dopt
s tar-‐shape
c onnection
m ethod
i n
c onstruction,
u nder
t his
s ituation,
t he
t erminal
r esistors
m ust
be
c onnected
b etween
t wo
f arthest
d evices
( as
F igure
A -‐9,
1 #
a nd
1 5#),
b ut
t his
c onnection
m ethod
i s
n ot
s atisfy
t he
requirement
o f
t he
R S485
i ndustry
s tandard
s o
t hat
i t
w ill
l ead
t o
s ome
p roblems
s uch
a s
s ignal
r eflection,
a nti-‐jamming
ability
d ecline
w hen
t he
d evices
a re
f araway.
A t
t his
t ime,
t he
d ome
w ill
b e
u ncontrollable,
o r
s elf-‐running,
e tc.
10225 Westmoor Drive, Suite 300, Westminster, CO 80021 | w ww.3xlogic.com | (877) 3XLOGIC
Max.
D istance
o f
R S485
T ransmission
Baudrate
2400BPS
4800BPS
9600BPS
2#
3#
Figure
A -‐7
R S485
C onnection
1
B -
A +
1 #
Figure
A -‐8
R S485
C onnection
2
Installation Manual |
V ISIX
P TZ
N etwork
C amera
Max
D istance
1800m
1200m
800m
4#
2 #
3 #
120Ω
32#
31 #
36
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