SC2000 PTA1587X, User Instruction

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4.4 RS485 Bus Wiring
1. RS485 bus basic characteristic
RS485 industry bus is characteristic impedance 120 Ω half-duplex
communication bus according to RS485 industry bus standard.
2. RS485 bus transmission distance
When use 0.511mm (24AWG) screen twisted pair cable as communication
cable. Depending on different baud rate, the longest transmitting distance
theoretical value is shown as below:
The longest transmitting distance of baud rate
2400Bps 1800m
4800Bps 1200m
9600Bps 800m
3. Connection mode and terminal resistance
RS485 industry bus standard require adopt snake-like wiring(chrysanthemum
chain), The ends must connect with 120 Ω terminal resista nce(such as figure 6),
ease connection can adopt figure 7, but distance of section “D” can’t exceed 7m.
1#
120
Ω
120
Ω
2# 3# 4#
……
……
……
32#
1#
D
A+
A+
B-
B-
2# 3# 31#
Fig6
Fig7
main control equipment
Chapter 4
Appendix
A
p
p
e
n
d
ix