COP-USA CD66MK-HW - Manual (Page 32)

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Appendix
Ⅲ Ⅲ Ⅲ Ⅲ
. RS485 Bus Basic Knowledge
1. Connection and termination resistor
The RS485 standards require a daisy-chain connection between the equipment. There must be
termination resistors with 120Ωimpedance at both ends of the connection .
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:
Baud Rate Maximum Transmitting Distance
2400 Bps 1800m
4800 Bps 1200m
9600Bps 800m
3. Connection and termination resistor
The RS485 standards require a daisy-chain connection between the equipment. There must be
termination resistors with 120Ωimpedance at both ends of the connection (refer to Picture 31).
Please refer to Picture 20 for simple connection. “D” should not exceed 7m.
120Ω 120Ω
1# 2# 3# 4# 32#
. . . . .
Figure 31
120Ω
1# 2# 3# 31#
120Ω
D
A+
B-
A+ B-
. . . . .
. . . . .
Main controller
Figure 29