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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
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+48
VDC Common
TB2
TB2
Power Supply
RTU 8130 with 8230 expansion module
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