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Modbus TCP problem - Printable Version

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Modbus TCP problem - judgment - 01.04.2026

hello please help. It seams that LM do not initiate any modbus tcp read request to modbus slave device. Tested with modbus Poll all works fine. 
Tried firmware upgrade - same issue. 
any ideas?Smile

   
   

RE: Modbus TCP problem - admin - 02.04.2026

See if you can ping Modbus device IP address from System config > Status > Network utilities.

RE: Modbus TCP problem - judgment - 02.04.2026

(Yesterday, 10:39)admin Wrote: See if you can ping Modbus device IP address from System config > Status > Network utilities.

hi tested - 4 packets transmitted, 0 packets received, 100% packet loss. Both, LM and other device i can access via http. Do you have a clue?

RE: Modbus TCP problem - AEK - 03.04.2026

(Yesterday, 19:00)judgment Wrote:
(Yesterday, 10:39)admin Wrote: See if you can ping Modbus device IP address from System config > Status > Network utilities.

hi tested - 4 packets transmitted, 0 packets received, 100% packet loss. Both, LM and other device i can access via http. Do you have a clue?

what IP settings are on LM and on your Modbus tcp device (IP, Netmask, Gateway)

RE: Modbus TCP problem - judgment - 03.04.2026

(Today, 06:16)AEK Wrote:
(Yesterday, 19:00)judgment Wrote:
(Yesterday, 10:39)admin Wrote: See if you can ping Modbus device IP address from System config > Status > Network utilities.

hi tested - 4 packets transmitted, 0 packets received, 100% packet loss. Both, LM and other device i can access via http. Do you have a clue?

what IP settings are on LM and on your Modbus tcp device (IP, Netmask, Gateway)

LM:                   192.168.1.3, 255.255.255.0, 192.168.1.1
Modbus device : 192.168.1.4, 255.255.255.0, 192.168.1.1


Same subnet. Both devices are reachable from my PC, and ping works 100%.

RE: Modbus TCP problem - admin - 03.04.2026

How are both devices connected? Switch or router? Maybe there is a firewall or port isolation is enabled.