HIKVISION IR Network Speed Dome, Руководство по установке, Страница: 35 / 38

IR Speed Dome Installation Manual
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Appendix 2 RS485 Bus Connection
1. RS485 Bus Properties
RS485 is a half-duplex communication bus which has 120Ω characteristic impedance, and its
maximum load ability is 32 payloads (including controlling devices and controlled devices).
2. RS485 Bus Transmission Distance
Using 0.56mm (24AWG) twisted-pair line, the max transmission distances for different baud rates
are shown as below:
Baud Rate Max Distance
2400BPS 1800m
4800BPS 1200m
9600BPS 800m
Table 4.1 Matched Resistance Settings
The transmission distance may decrease if a thinner cable is used, or the device is under a strong
electromagnetic interference, or a bus is shared by multiple devices; vice versa.
3. RS485 Bus Connections
According to the industry standard, daisy-chain connection can be adopted for RS485 bus
connections, with a 120Ω terminal resistor connected to both ends (as shown in Diagram 1). A
simplified connection can also be applied in the cases that distance “D” is within a limited range (as
shown in diagram 2).
Figure4. 2 Daisy-chain Connection