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Table of contents
1 Introduction ....................................................................................................................................................... 3
1.1 Intended audience .......................................................................................................................................... 3
1.2 Before you start .............................................................................................................................................. 3
1.3 How to use this manual ................................................................................................................................. 3
2 Overview ............................................................................................................................................................. 4
2.1 Introduction to Modbus ................................................................................................................................ 4
2.2 The Modbus adapter ...................................................................................................................................... 4
2.3 Compatibility................................................................................................................................................... 4
3 Serial interface considerations ...................................................................................................................... 5
3.1 Communication mode ................................................................................................................................... 5
3.2 SINGLE ENDED versus DIFFERENTIAL data transmission ....................................................................... 5
3.3 RS-232 interface .............................................................................................................................................. 6
3.4 RS-422 interface .............................................................................................................................................. 6
3.5 RS-485 interface ............................................................................................................................................. 6
3.6 Bias resistors ................................................................................................................................................... 7
3.7 Termination resistors .................................................................................................................................... 7
3.8 Shielding and grounding considerations ................................................................................................... 7
3.9 Cable requirements ........................................................................................................................................ 7
3.10 Network topology........................................................................................................................................... 8
4 RS485 Modbus adapter ................................................................................................................................... 9
4.1 Main features .................................................................................................................................................. 9
4.2 Physical dimensions ....................................................................................................................................... 9
4.3 Mounting ........................................................................................................................................................ 10
4.4 Technical data ............................................................................................................................................... 10
4.5 Commissioning process ............................................................................................................................... 11
4.6 To set the COMMUNICATION LOCK parameter ........................................................................................ 12
4.7 To test the communication.......................................................................................................................... 12
5 Modbus protocol overview ........................................................................................................................... 13
5.1 Overview .........................................................................................................................................................13
5.1.1 Transactions on Modbus Networks .........................................................................................................13
5.1.2 Serial Transmission Mode .........................................................................................................................13
5.2 Data Addresses in Modbus Messages ...................................................................................................... 14
5.3 Supported function codes .......................................................................................................................... 14
6 Data access ...................................................................................................................................................... 15
6.1 Access levels .................................................................................................................................................. 15
6.2 Minimum and maximum values .................................................................................................................. 15
6.3 Modbus Data table ....................................................................................................................................... 15
7 Troubleshooting ............................................................................................................................................. 16
7.1 Preferred method of testing....................................................................................................................... 16
7.2 Check of identical Slave – Master configuration ..................................................................................... 16
7.3 Check the cabling of the RS485 ................................................................................................................... 17
7.4 Check the Transmit – Receive indicators ................................................................................................... 17
7.5 Check the function called and the register addresses ............................................................................ 17
7.6 Check the data access level and the limited range of data ................................................................... 18
7.7 Counters and Loopback diagnostics ........................................................................................................ 18
7.8 Debugging tool and documents ................................................................................................................ 18
8 Appendices ...................................................................................................................................................... 19
A1 List of abbreviations ....................................................................................................................................... 19
A2 References ......................................................................................................................................................... 21
A3 Adequate choice of an RS232-RS485 converter at the computer side ................................................... 22
2 Table of contents ç RS485
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