DM-1001 SMA — RS485 Communication Failure
At a glance
- Severity
- WARNING
- Domain
- MONITORING_COMM
- Reference standard
- EIA/TIA-485 / Modbus RTU
- Product / context
- Device Communication Error (RS485)
What it means
Fault on the RS485/Modbus RTU serial communication between the datalogger and field devices (inverters, meters, sensors). One or more devices are not communicating.
Probable causes
- A/B wire polarity reversed on one or more bus nodes.
- 120 ohm termination resistor missing or incorrectly positioned.
- Baud rate or serial parameters (parity, stop bit) not uniform across devices.
- Modbus address conflict: two devices with the same slave ID.
Reference values
| RS485 | {"termination":"120 Ω at the two bus ends only","polarity":"A/B (D+, D−)","max_nodes":"32 per segment","typical_baud":"9600-115200","nota":"Replace the cable with shielded twisted pair in noisy environments."} |
|---|
Where to start
Check the RS485 wiring: verify the A(+) and B(-) wire polarity on every device, cable continuity, and shield grounded at one point only. Is the wiring correct?
Full guided diagnosis in the app
The diagnostic tree for this fault has 7 guided steps with measurements, checks and resolutions. You'll find it in ElectraIQ, one of the five IndexOS apps: free, works offline.
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