Modbus TCP/IP connection failure


Thread Starter


I am testing MODBUS communication between PLC and DCS

slave is GE MARK system and master is ABB CI867 module. Whenever I disconnect cable and reconnect, DCS can't find slave( no response from slave : status code: -7006)

if any of you have some experiences can you help me?


Lynn August Linse

Maybe a TCP Keepalive issue - pulling the cable like that can break the TCP socket in such a way that one end doesn't realize it's broken (usually the slave). Thus when the Master returns and tries to reconnect, the slave in effect is 'busy' still linked to the old dead socket & rejects the 'second' master trying to connect.

TCP keepalive (sadly often off by default) is designed to detect such idle Sockets and free them.

I have no idea how one would enable these on the devices you mention.