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
