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Chapter 3
Two-Wire Networks
Master Device
R
*
T
T--
R--
T+
R+
Gnd
EATON Powerware
Wiring the Modbus Card
The Modbus Card provides an easy path for integrating a Powerware
UPS into an RS-485 Modbus network and also provides isolation of the
communication between the UPS and the RS-485 Modbus network.
You can use the DB-9 port or terminal strip on the Modbus Card to wire
into a two-wire or four-wire network.
The Modbus Card's default configuration is for two-wire, half-duplex,
RS-485 networks. Figure 6 shows a detailed view of two-wire
connections using the Modbus Card terminal strip.
Slave Device #1
Slave Device #2
T--
R--
T+
R+
Gnd
Figure 6. Two-Wire RS-485 Modbus Network
NOTE Only one transmission pair is used. It is not necessary to jumper the unused pair
together (this connection is made internally). Belden 9841 or equivalent cabling (a single
twisted-pair shielded cable with ground) is recommended.
NOTE If the Modbus Card is the last device installed in the network chain or the length of
the network cable is excessive, termination needs to be enabled (see page 10).
®
®
Modbus
Card User's Guide
UPS with
Modbus Card
T--
R--
T+
R+
Gnd
S
164201376 Rev C www.powerware.com
RxD+
RxD–
R
*
T
*See Note
7
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