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4.4 RS485 Bus Wiring
RS485 bus basic characteristic
RS485 industry bus is characteristic impedance 120Ω half-duplex communication bus
according to RS485 industry bus standard.
RS485 bus transmission distance
When using 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
Connection mode and terminal resistance
RS485 industry bus standard require adopt snake-like wiring (chrysanthemum chain), the
ends must connect with 120Ω terminal resistance(such as figure 6), ease connection can
adopt figure 7, but distance of section "D" can't exceed 7m.
18
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