HD-TVI Speed Dome DS-2AE7232TI-A User Manual
UM THD DS-2AE7232T-x 020519NA 42
Appendix 2 RS-485 Bus Connection
• General Property of RS-485 Bus
According to RS-485 industry bus standard, RS-485 is a half-duplex communication bus that has 120 Ω
characteristic impendence. The maximum load ability is 32 payloads (including controller device and
controlled device).
• RS-485 Bus Transmission Distance
When using 0.56 mm (24 AWG) twisted-pair line, according to different baud rate, the maximum
transmission distance theory table is shown as below:
Table A-1 Maximum Distance of RS-485 Transmission
Baud Rate Maximum Distance
2400 bps 1800 m
4800 bps 1200 m
9600 bps 800 m
The transmission distance will be decreased if we use thinner cable, use this product under a strong
electromagnetic interference situation, or lots of devices are added to the bus; on the contrary, the
transmission distance will be increased.
• Connection Methods
RS-485 industry bus standard requires a daisy-chain connection method between devices, both sides
have to connect a 120 Ω terminal resistance (shown as Diagram 1). A simplified connection method is
shown in Diagram 2, but the distance of “D” should not be too long.
Figure 26, RS-485 Connection 1
Figure 27, RS-485 Connection 2
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