CI867 as Slave
Is it possible to add two cards CI867 both acting as slave, for two master.
Both accessing same data from the access variable
Yes in theory it should be. It is up to you to control which system can read or write to the variable.
However, the Modbus TCP standard supports multiple masters - you just have to ensure only one is writing to a variable. So - in theory - you should only need one CI867. Theres no information in the manuals about whether this is supported or not. If this doesnt work you could probably use a Moxa MGate modbus gateway.