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Section 5. System Overview

5.3.10.1 Modbus

Related Topics:

• Modbus — Overview (p. 91)

• Modbus — Details

(p. 411)

The CR1000 supports Modbus master and Modbus slave communications for

inclusion in Modbus SCADA networks. Modbus is a widely used SCADA

communication protocol that facilitates exchange of information and data between

computers / HMI software, instruments (RTUs) and Modbus-compatible sensors.

The CR1000 communicates with Modbus over RS-232, RS-485 (with a RS-232 to

RS-485 adapter), and TCP.

Modbus systems consist of a master (PC), RTU / PLC slaves, field instruments

(sensors), and the communication-network hardware. The communication port,

baud rate, data bits, stop bits, and parity are set in the Modbus driver of the master

and / or the slaves. The Modbus standard has two communication modes, RTU

and ASCII. However, CR1000s communicate in RTU mode exclusively.

Field instruments can be queried by the CR1000. Because Modbus has a set

command structure, programming the CR1000 to get data from field instruments

is much simpler than from serial sensors. Because Modbus uses a common bus

and addresses each node, field instruments are effectively multiplexed to a

CR1000 without additional hardware.

5.3.10.2 DNP3 — Overview

Campbell CR1000 User Manual

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