Troubleshooting Modbus - Carrier RTU Open v3 Integration Manual

Wire specifications
A dedicated 22 AWG shielded twisted pair wire (EIA 485)
○
Maximum wire length 2000 feet (610 meters) or 32 nodes
○
Devices should be daisy-chained and not star-wired
○
Attach the drain/shield wire to both ends of the network segment and through every controller
○
NOTE Use the same polarity throughout the network segment.
7
Turn on the RTU Open's power.

Troubleshooting Modbus

Check the following to troubleshoot your RTU Open:
1
Verify that the BAS and controller are both set to speak the Modbus RTU protocol on the Comm Selector DIP
switches DS3 - DS6.
2
Verify that the BAS and the controller are both set for the same baud rate:
Baud rate DIP switches DS2 and DS1
○
Obtain a Modstat of the controller. Scroll to the bottom of the page to Network Communications to view
○
the active protocol and baud rate.
3
Verify that the BAS is configured to speak 2-wire EIA-485 to the controller. The BAS may have to configure
jumper or DIP switches on their end.
4
Verify that the BAS and the controller have the same communication settings (8 data bits, No Parity, and 1
stop bit).
5
Verify proper connection wiring between the BAS and the controller.
6
Verify that the rotary address switches are set for the controller's unique slave address.
7
BAS must be reading or writing to the proper point addresses on the controller.
8
BAS is sending requests to the proper slave address of the controller.
NOTES
•
Refer to Appendix A (page 35) for the Network Points list.
•
Refer to Appendix C (page 47) for the Protocol Implementation Conformance Statement.
Modbus Exception Codes that might be returned from this controller
Codes
01
02
04
RTU Open v3
Integration Guide
Name Description
Illegal Function The Modbus function code used in the query is not
supported by the controller.
Illegal Data The register address used in the query is not supported
Address by the controller.
Slave Device The Modbus Master has attempted to write to a non-
Failure existent register or a read-only register in the
controller.
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Communications wiring
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