Intesis
TM
INMBSMID---I000
User’s Manual r
1.3 EN
© HMS Industrial Networks S.L.U - All rights reserved
This information is subject to change without notice
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4.8
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.
In order to prevent fail status detections by the receivers, which are
"listening"
the bus, when
all the transmitters
’
outputs are in three-state (high impedance), a fail-safe biasing
mechanism is required. This mechanism provides a safe status (a correct voltage level) in the
bus when all the
transmitters’
outputs are in three-state.
The INMBSMID---I000 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 M
aster devices can provide also internal 120Ω terminator resistor
and/or fail-safe biasing. Check the technical documentation of the Master device connected to
the EIA-485 network in each case.
