48
Connect Devices
WAGO-TO-PASS® 761
761-217 Telecontrol Module Compact, 8 AI, Web, MODBUS485
Manual
Version 1.0.0
5.2.6
MODBUS Interface
MODBUS Line terminator
The MODBUS specification requires a line terminator at both ends of an RS-485
bus.
If the
TO-PASS
®
telecontrol module is operated at one end of the line, the
terminator must be added (e.g., directly in the D-Sub plug-in connector, or at the
bus terminals of interface module 289-966).
According to the specification, a 150
Ω resistor (0.5 W) or a 1nF capacitor (at
least 10 V) and a 120
Ω resistor (0.25 W) connected in series can be used for this.
If the
TO-PASS
®
telecontrol module is operated outside the bus (not at the end),
the branch cable must be kept as short as possible.
BIAS Network
Some RS-485 drivers require a BIAS network to ensure a constant status when
there is no transmission (active transmitter) on the bus.
The
TO-PASS
®
telecontrol module (as the MODBUS master) is equipped with a
BIAS network with two 470
Ω resistors (at GND and +5 V).
Connect shielding!
Shielded cables are required for MODBUS communication. The cable shield
must be connected to the DIN rail (see section "Connections" > "Shielding").
