Eia-485 Bus. Termination Resistors And Fail-Safe Biasing Mechanism - Intesis IntesisBox FJ-AC-MBS-1 User Manual

ModBus RTU – Fujitsu
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EIA-485 bus. Termination resistors and Fail-Safe Biasing mechanism

EIA-485 bus requires a 120Ω terminator resistor at each end of the bus to avoid signal reflections.
To prevent fail status detected by the receivers, which are "listening" the bus, when all the transmitters' outputs are
in three-state (high impedance), it is also required a fail-safe biasing mechanism. This mechanism provides a safe
status (a correct voltage level) in the bus when all the transmitters' outputs are in three-state. This mechanism must
be supplied by the Modbus Master.
The FJ-AC-MBS-1 device includes an on-board terminator resistor of 120Ω that can be connected to the EIA-485
bus by using DIP-switch SW4.
Some Modbus RTU EIA-485 Master devices can provide also internal 120Ω terminator resistor and/or fail-safe
biasing mechanism (Check the technical documentation of the Master device connected to the EIA-485 network in
each case).
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User Manual r1.0 EN
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