4 modbus connections, 5 diagnostic connection, 6 wiring rules - modbus networks – GE GEH6505A User Manual

Page 10: Chapter 2 – installation, Power leader™ ethernet gateway, 2–4 modbus connection, 2–5 diagnostic connection, 2–6 wiring rules – modbus networks

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POWER LEADER™ Ethernet Gateway

Chapter 2 – Installation


2–4 Modbus Connection

The Modbus RTU networks should be connected to

the RS485 ports on the back of the Ethernet

Gateway, as shown in Figure 9.

Figure 9. Connecting an RS485 network to the Ethernet


Per the EIA-485 standard, the RS485 networks must

be terminated at both ends. Position the Ethernet

Gateway at one end of the RS485 networks, as it is

internally terminated. The user must ensure that

the final device on each network is terminated

correctly, as shown in Figure 10.

Figure 10. Terminating an RS485 network at the last device.

2–5 Diagnostic Connection

The RS232 port on the back of the Ethernet

Gateway is provided for connection of a dumb

terminal to the Gateway. The terminal may be used

for configuring the Ethernet Gateway’s settings or

for diagnostic purposes. For diagnostic purposes,

the Gateway may be set to display all messages and

traffic on the terminal so that problems may be

tracked down and corrected. To connect a terminal

(usually a laptop computer running Windows’

Terminal accessory software) to the Gateway, plug

its RS232 cable into the RS232 port on the back of

the Ethernet Gateway, as shown in Figure 11.

Figure 11. Connecting a dumb terminal to the RS232 port.

2–6 Wiring Rules – Modbus Networks

When wiring Modbus RTU devices to an Ethernet

Gateway, follow the wiring rules below to ensure

proper configuration. Refer to GEH-6502, the PMCS

Network Architecture Guide

, for specific examples of

correct and incorrect configurations.
1. Up to 31 Modbus devices may be attached to a

single Modbus network. RS485 repeaters do not

have Modbus addresses, but do count as devices

toward the 31 physical devices per network limit.

2. Every device on a single Modbus network must

have a unique address. (Devices on different

networks may use the same Modbus address,

i.e., it is acceptable to have a device addressed as

device 10 on Network 1 and another device

addressed as device 10 on Network 2.) Use the

Modbus address worksheets (at the end of this