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+--- Thread: Modbus communication lost (/showthread.php?tid=4269)
Modbus communication lost - kurt-erik.rauset@caverion.com - 28.09.2022
Hi!
I had som modbus profiles who worked fine on two different ports.
Then i added som datapoints from KNX and connected a new component to one of the ports.
Suddenly all modbus communication is lost. I can`t find any components either with RTU Scan og Read test.
What is wrong?
Is there any posibility to vclear or reset the modbus ports?
RE: Modbus communication lost - Daniel - 28.09.2022
Check wiring, maybe you shorted something.
RE: Modbus communication lost - DarthPaul - 29.09.2022
But if you short RTU port 1.
Would that also affect RTU port 2?
Here everything is down after working on 1 of 2 ports.
Will LM5 block all modbus RTU if there is a serious enough fault on 1 port?
RE: Modbus communication lost - Daniel - 29.09.2022
Yes
RE: Modbus communication lost - admin - 29.09.2022
First, check Modbus error log. There's a slight chance that some incorrect profile definition causes Modbus mapper to crash. Have you tried rebooting LM to see if Modbus starts working?
If daemon is running then disconnect both lines and connect only one device and see if it works.
You can also disable both Modbus ports, connect RS485 1/2 together and run self test to check that ports are working: https://forum.logicmachine.net/showthread.php?tid=3355&pid=21682#pid21682
RE: Modbus communication lost - DarthPaul - 29.09.2022
Thanks for advice. We did all that. And it didn't help.
BUT; we changed borth ports from Full-Duplex to Half-Duplex
And now everything works.
Am not sure if both were Half-duplex before and some-one/thing changed this to Full-duplex..
But it is all running on half atleast..
RE: Modbus communication lost - admin - 29.09.2022
RS485 is a half duplex connection. Setting full duplex mode will prevent ports from working correctly. For RS485-2 full duplex mode enables RS232 instead of RS485.
RE: Modbus communication lost - jeroen@stevens.biz - 31.10.2022
One one of my LM I have a Modbus RS485 issue. I can get out data 1 out of 2 times. One call goes OK and I get data, second call results in a CRC error. I tried this with a readtest under Modbus. When I get a CRC error, the communication LED on the Janitza unit flashes green (that is OK).
With a profile that works on my other LM everything goes right.
I want to read out a Janitza power meter UMG20CM (it has a communication led), this device has Modbus address 1, speed 9600
I tried the following things:
a/ reverse polarity (then always crc errors, red error led on Janitza meter for communications)
b/ connect GND of LM and Janitza: no difference
c/ checked if the fase and neutral of the LM and Janiza aren't switched
d/ tried to lower speed 38400 --> 9600
e/ tried parity al variants (now no, 1 stopbit)
f/ tried other cabling, twisted pair stranded cable
Any tips to try?
RE: Modbus communication lost - admin - 01.11.2022
Have you tried using a different RS485 port on LM?
RE: Modbus communication lost - jeroen@stevens.biz - 20.11.2022
Sorry for the late answer. The problem is that this is on a remote location (>500 km). I didn't try the other port yet.
Any other suggestions?
RE: Modbus communication lost - admin - 21.11.2022
Try running Modbus debug script and post what you get: https://forum.logicmachine.net/showthread.php?tid=3997&pid=25802#pid25802
Adjust settings as needed and add an additional read to make it behave similar to the mapper where you get the CRC error.