just another question to the Modbus TCP: According to manual the system variable MBTCP_M.Conn hold the number of active connections.
Considering a setup with redundant CPU and redundant slaves, I observe ther following
- the value of MBTCP_M.Conn is '1' or '2'. I do not understand when it is '1' and when '2'. In our system I can see, that the inactive slave does not get any Modbus Requests, so I would assume, Freelance CPU connects to the inactive slave just after the active one gets lost.
- the value drops to 0 whenever I interrupt the active line, irrespective that the inactive line is intact and available. After few seconds it comes back to '1' when the backup line is activated.
I tried to use the value to implement an application based CPU switchover, and it is possible using a delay timer. But still I'd like to understand the real meaning of this variable.
Can you give me more information here?
Thanks & best regards
Voted best answer
The master has only a connection to one of the IP addresses at a time. It only switches to the second slave address if the connection to the primary slave address gets lost.