ABB EC Titanium Series - Appendix A Modbus-RTU Example Connection

Modbus-RTU Example Connection A-1MN448
Appendix A
Modbus-RTU Example Connection
Overview
This chapter gives specic details on how to use Modbus RTU as the communication protocol of the IMD. Below you will
nd register mapping, telegram structure, and connection details.
ACS255 drives support Modbus RTU communication, allowing a network of drives to be controlled and monitored by any
Modbus RTU capable PLC or control system. The drive is always a Slave to an external Modbus RTU Master. This document
describes the registers and functions available.
A.1 Modbus RTU Communications
Introduction
The IMD can be connected to a Modbus RTU network via the RJ45 connector or the control terminal strip.
A.2 Modbus RTU Specification
Protocol Modbus RTU
Error check CRC
Baud rate 9600bps, 19200bps, 38400bps, 57600bps, 115200bps (default)
Data format 1 start bit, 8 data bits, 1 stop bits, no parity.
Physical signal RS 485 (2-wire)
User interface RJ45 (see section A.5 for more information)
A.3 RJ45 Connector Configuration
Connection details are shown in section A.5.
A.4 Modbus Telegram Structure
The following Modbus RTU Commands are supported
• 03 Read Holding Registers
• 06 Write Single Holding Register
The telegram structure is as follows:
Command 03 – Read Holding Registers Command 06 – Write Single Holding Register
Master Telegram Length Slave Response Length Master Telegram Length Slave Response Length
Slave Address 1 Byte Slave Address 1 Byte Slave Address 1 Byte Slave Address 1 Byte
Function Code (03) 1 Byte Function Code (03) 1 Byte Function Code (06) 1 Byte Function Code (06) 1 Byte
1st Register Address 2 Bytes Data Length 2 Bytes Register Address 2 Bytes Register Address 2 Bytes
No. Of Registers 2 Bytes 1st Register Value 2 Bytes Value 2 Bytes Register Value 2 Bytes
CRC Checksum 2 Bytes 2nd Register Value CRC Checksum 2 Bytes CRC Checksum 2 Bytes
Etc...
CRC Checksum 2 Bytes