i have three devices with an IP address 192.168.0.125, port 502 and device IDs 1, 2 and 3 on modbus protocol. I need to write a software routine that after a fixed interval polls to check the health status of the connection with three devices. which function code should i use? all the devices have the same ip and port number... I can't use the diagnostic functions as they are only supported on serial line... Any directions??

 

The IP address given sounds like the factory default. You will need to start by changing each IP address so each is unique. Since these will all be on the same network, which I assume is separate from any other Ethernet nodes, the first three fields should be the same with a unique number for each in the fourth field. You will need to check your device documentation to see how you can change your IP address. You may need a bootp utility or possibly need to connect to each device directly (one at a time) and via the given IP address use your browser to see if configuration access is available.

Robert D. Wagner, P.E.