Rs485 Bus Connection - HIKVISION Positioning System User Manual

User Manual of Thermometric Bi-spectrum Network Positioning system
Appendix 3 RS485 Bus Connection
 General Property of RS485 Bus
According to RS485 industry bus standard, RS485 is a half-duplex communication bus
which has 120Ω characteristic impendence, the maximum load ability is 32 payloads
(including controller device and controlled device).
 RS485 Bus Transmission Distance
When using 0.56mm (24AWG) twisted-pair line, according to different baudrate, the
maximum transmission distance theory table is shown as below:
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 Diagram
1), the simplified connection method is shown as diagram 2, but the distance of
"D" should not be too long.
120Ω
1#
A+
D
B-
Controller
 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#), but this connection method is not satisfy the requirement of
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Max. Distance of RS485 Transmission
Baudrate
2400BPS
4800BPS
9600BPS
2#
Figure A-7 RS485 Connection 1
A+ B-
1#
Figure A-8 RS485 Connection 2
Max Distance
1800m
1200m
800m
...
3#
2#
134
120Ω
32#
...
31#