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+--- Thread: Modbus device status object stuck at 0 (/showthread.php?tid=6499)
Modbus device status object stuck at 0 - p_xatzi - 02.07.2026
Hi,
I have a LΜ5 Lite (Version: 20240426) polling 33 Modbus TCP servers (Siemens LOGO! OBA8), each on a 10-second polling interval.
I'm having a problem with the Modbus status object for these devices. It gets set to 0 at some point, but then it is never set back to 1 when communication is restored (if ever lost) — even though the device is clearly communicating as indicated in Modbus tab.
If I manually reset the status object to 1, it stays at whatever I set it to — it does not get corrected by the driver on the next successful poll. This suggests the driver only writes to it on a state change (communication lost / restored), not on every poll cycle.
In addition, I noticed that the status object drops to 0 exactly at the moment another mapped value on the same server changes, even though that data object is unrelated to the status object. In other words, receiving new data from the device seems to coincide with the status going down.
In my own scripts I never write to these status objects — I only read them.
My questions:
Is there a known issue where the Modbus device status object goes to 0 when new data is received from the server, or when a mapped value changes?
Since the status appears to be updated only on lost/restored events, what happens if a "restored" event is somehow missed — is the object then left permanently at 0?
What is the recommended way to obtain a reliable, real-time connection status for each Modbus TCP device?
Thanks
RE: Modbus device status object stuck at 0 - admin - 02.07.2026
Post what you have in the Modbus error log.
RE: Modbus device status object stuck at 0 - p_xatzi - 03.07.2026
(02.07.2026, 12:12)admin Wrote: Post what you have in the Modbus error log.Hi Admin,
Unfortunately, the error log is currently flooded with entries coming from a server that is disconnected. I have already completed the setup for future use, so I do not want to delete it; however, I am not sure how to simply disable it.
From what I can see, the Modbus error log has a maximum capacity of about 250 entries and currently displays only today's errors.
Thanks
RE: Modbus device status object stuck at 0 - admin - 03.07.2026
You can temporary increase the poll interval to a large value for this server.
RE: Modbus device status object stuck at 0 - p_xatzi - 03.07.2026
(03.07.2026, 10:09)admin Wrote: You can temporary increase the poll interval to a large value for this server.
I have set poll interval to maximum allowable setting, that is 1800 sec.
So, I will send you the error log as soon as the same issue appears again.
However, I just received a notification (which triggers whenever the status object changes state) indicating that communication has been restored. Specifically, there were 3 servers with the wrong flag, and all of them were restored concurrently. Therefore, I assume the driver must have updated these values based on an internal clock or a similar mechanism. Could you explain how this works?
Thanks.