ABB RS485 - Default Chapter; Table of Contents

2 – Table of contents  RS-485
Table of contents
1 Introduction .................................................................................................................. 4
1.1 Intended audience ................................................................................................. 4
1.2 Before you start ..................................................................................................... 4
1.3 How to use this manual ......................................................................................... 4
2 Overview ....................................................................................................................... 5
2.1 Introduction to Modbus .......................................................................................... 5
2.2 The Modbus adapter ............................................................................................. 5
2.3 Compatibility .......................................................................................................... 5
3 Serial interface considerations................................................................................... 6
3.1 Communication mode ............................................................................................ 6
3.2 SINGLE ENDED versus DIFFERENTIAL data transmission ................................ 6
3.3 RS-232 interface .................................................................................................... 6
3.4 RS-422 interface .................................................................................................... 7
3.5 RS-485 interface .................................................................................................... 7
3.6 Bias resistors ......................................................................................................... 7
3.7 Termination resistors ............................................................................................. 7
3.8 Shielding and grounding considerations ............................................................... 8
3.9 Cable requirements ............................................................................................... 8
3.10 Network topology ................................................................................................... 8
4 RS485 Modbus adapter ............................................................................................. 10
4.1 Main features ....................................................................................................... 10
4.2 Physical dimensions ............................................................................................ 10
4.3 Mounting .............................................................................................................. 11
4.4 Technical data ..................................................................................................... 11
4.5 Commissioning process ...................................................................................... 12
4.6 To set the COMMUNICATION LOCK parameter ................................................ 13
4.7 To test the communication .................................................................................. 13
5 Modbus protocol overview ....................................................................................... 14
5.1 Overview .............................................................................................................. 14
5.1.1 Transactions on Modbus Networks ............................................................. 14
5.1.2 Serial Transmission Mode ........................................................................... 14
5.2 Data Addresses in Modbus Messages ................................................................ 15
5.3 Supported function codes .................................................................................... 15
6 Data access ................................................................................................................ 16
6.1 Access levels ....................................................................................................... 16
6.2 Minimum and maximum values ........................................................................... 16
6.3 Modbus Data table .............................................................................................. 16
7 Troubleshooting ......................................................................................................... 17
7.1 Preferred method of testing ................................................................................. 17
7.2 Check of identical Slave – Master configuration ................................................. 17
7.3 Check the cabling of the RS485 .......................................................................... 17
7.4 Check the Transmit – Receive indicators ............................................................ 18
7.5 Check the function called and the register addresses ........................................ 18
7.6 Check the data access level and the limited range of data ................................. 18
7.7 Counters and Loopback diagnostics ................................................................... 19
7.8 Debugging tool and documents ........................................................................... 19
8 Appendix ..................................................................................................................... 20
8.1 List of abbreviations ............................................................................................. 20