XVision XPS036, Руководство пользователя

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1. CHARACTERISTICS OF RS485 BUS
As specified by RS485 standards, RS485 Bus is of half-
duplexed data transmission cables with characteristic
impedance as 120 Ohm. The maximum load capacity is
32 unit loads (including main controller and controlled
equipment).
2. TRANSMISSION DISTANCES OF RS485 BUS
When user selects the 0.56mm (24AWG) twisted pair
wires as data transmission cable,the maximum theoretical
transmitting distances are as follows:
If user selects thinner cables, or installs the dome in an
environment with strong electromagnetic interference, or
connects lots of equipment to the RS485 Bus, the maximum
transmitting distance will be decreased. To increase the
maximum transmitting distance, do the contrary.
3. CONNECTION AND TERMINATION RESISTOR
3.1 Daisy Chain Connection
The RS485 standards require a daisy-chain connection
between the equipment. There must be termination resistors
with 120 Ohm impedance at both ends of the connection
(refer to following pictures).
Please refer to below picture for simple connection. Distance
“D” should not exceed 7 meters.
3.2 The connection of 120 Ohm termination
resistor:
The termination resistor is ready on the Protocol PCB. There
are two kinds of connection. Please refer to the Protocol PCB
jumper setting form (refer to following pictures).
a) In the Picture it is the factory default connection.
The jumper is seated on Pin 2 & Pin 3 and the termination
resistor is not connected.
b) when connecting the 120 Ohm termination resistor,
user should pull out the protocol PCB and plug the
jumper on Pin 1 & Pin 2.
Install the PCB back and the termination resistor is
connected.
Appendix 3: RS485 Bus Basic Knowledge
Baud Rate Transmission Distance (Max.)
2400bps 5,906ft (1800m)
4800bps 3,937ft (1200m)
9600bps 2,625ft (800m)
2 3 1 2 JP1
OFF ON 120 Ohm
3 2 1
JP1
3 2 1
JP1
120 Ω 120 Ω