Varec Network Adapter 4000, Installation And Operation Manual, Page: 17 / 80

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4000 Installation
2.4.5 ATT EIA485 Wiring
The ATT uses a 2-wire EIA485 hardware interface to communicate with the Modbus
master. EIA485 is a high speed differential communications network which allows up to
32 devices to operate on one network. The ATT and Modbus master share a twisted pair
of wires to communicate. Figure 2-4 illustrates the typical EIA485 wiring.
The communication distance that EIA485 can reliably travel is dependent on baud rate
(communication speed), wire quality, environmental noise, wiring configuration, and the
number of multi-dropped ATTs. The recommended wire for EIA485 systems is
18-gauge or larger, shielded, twisted pairs. The shield should be earth grounded at the
Modbus master (control system or computer end). The shield at the ATT should be open.
The ATT B- power line acts as a common reference tie to the Modbus master. Figure 2-5
on page 8 illustrates the EIA485 Modbus system.
Figure 2-4: Typical EIA485 Wiring
6
+48
VDC
Common
TB2
TB2
Power Supply
RTU 8130 with 8230 expansion module
5
4