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2 Overview
This chapter contains a short description of the Modbus protocol and the RS485
interface.
2.1 Introduction to Modbus
Modbus is a serial, asynchronous protocol. The Modbus protocol does not specify the
physical interface. The typical physical interfaces are RS-232 and RS-485. The Interface
Module uses the RS-485 interface.
Modbus is designed for integration with PLCs or other automation devices, and the
services closely correspond to the PLC architecture.
The Modbus commands and services supported by the Modbus adapter are discussed
in Chapter 5.
2.2 The Modbus adapter
The Modbus adapter is an optional device for the Power Factor Controller RVT
Touchscreen which enables the connection of the RVT to a Modbus system. The
controller is considered as a slave unit in the Modbus network.
Through the Modbus adapter it is possible to:
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Read measurements and logged values
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Read and write parameters settings of the controller
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Activate output relays
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Read status information
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Read device identification and type numbers
2.3 Compatibility
The Modbus adapter is compatible with any Power Factor Controller RVT Touchscreen.
Other ABB controllers may be connected with the adapter.
CAUTION: Be careful that the RS485 MODBUS ADAPTER is the one with a GREEN text
colour (3.3V power supply). The one with a WHITE text colour is reserved for the old
model (5V power supply).
The Modbus protocol is compatible with all master stations that support the Modicon-
defined Modbus serial communication protocol.
4 Overview ç RS485
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