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Hello
I am new to this, and would need some more help: I try to read a device using modbus TCP. I can ping the device, but cannot read any registers from it. Whatever I try, I get Error: Communication Failed message in the Line Log/Stat. With localhost + ModbusSimulator the project is working, but as soon I try to connect to this device, I got error. I read it somewhere here in another topic/comment that the Byte Order can affect this..? Or it has nothing to do with Communication errors.. I tried many things: connected directly, disabled firewall, and yes – watched the modbus videos, etc.
Any advice would be appreciated. Will upload photos and logs tomorrow. Thanks, GaborIf you don’t see any bytes transmitted from the device in the log, then there is a problem with the connection.
Thank you for your reply. This is what I am thinking too.. Unfortunately can’t figure it out what the problem can be. Changed the IP address from localhost to the device IP in the project file (in 2 places), is there anything else to do? Target Device responses to ping and also tested port 502 with telnet command. Direct connection with lan cable, firewall off.
show the log of a specific device. what data goes into it. is the device responding or just a timeout error?
show the line and device settings.
No,it looks like it does not respond at all (sending data continuously but 0 response). I started all from zero as shown in the modbus video and all worked with the simulator, however not worked on a real device. Will attach files in the afternoon as I am currently not near the setup.. Thanks in advance
Hello, here are the photos:
Line state:
https://i.postimg.cc/vH2Nx8Fz/image.jpgLine log:
https://i.postimg.cc/FHfnythK/image.jpgDevice:
https://i.postimg.cc/FK3W6jfw/image.jpgDevice polling:
https://i.postimg.cc/0QvW1bDP/IMG-20260412-161625-765-jpg-adding.jpgI am guessing it is just some silly mistake from me..
Some more photos of the config:
Device config:
https://i.postimg.cc/C5xgCFhW/image.jpgLine Main options:
https://i.postimg.cc/gJYFdYZr/image.jpg(Don’t worry about the 103…104 numbering, after getting errors, I tried with the next physical Device (103 -> 104), but did not change the project/device name, etc. Only the IP)
And start with one register, specifying in the settings to start with 0 or 1. Do you also have the exact device address = 1 ? Depending on the device, the device ID may be ignored in Modbus TCP mode, or it may have to correspond to some value.
Yes I tried with one register,and had same result. Thanks, I will try to change the device ID,maybe it is not 1. I assume I should change the Numeric Address in the device settings.. The device itself has Zero based Addresses, starting with a 32bit unsigned integer for Timestamp,the other holding registers are float type. Requesting the wrong type,address,etc. could also cause “Error:Communication failed” message?
Yes, if the address requires 0 for the device, this may be the reason. Another option is to send a broadcast address to the device – 254 or 255 in Modbus mode when it is connected to TCP. Such things should be specified in the device documentation.
Unfortunately I am not familiar with sending broadcast address,etc. The device documentation is very poor,or lets say simple (as per above): Zero Based Addresses for Holding registers (I received the register mapping), static IPs for the devices. But I think I have to dive deeper into this.
Hi,
According to the communication line log you can successfully connect to the device by IP, but it is not responding.
I suppose the device ID (unit ID) is wrong as written above. Most common are 0 and 1.
Use https://rapidscada.net/modbus/ to decode data packets. It is useful for understanding.
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