Those control systems can reliably access the variables of the other party when two CPUs communicate over Ethernet
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The control systems of those brands can reliably access the variables of the other CPU when the two CPUs communicate over Ethernet, thereby enabling interlocking for device control. Including PLC and DCS.
I don’t think it’s difficult; after all, communication between devices of the same brand is much more reliable than that between devices of different brands
For some brands, a simpler communication approach may result in higher reliability, while this is not the case for others. For example. Between Siemens S7-400 CPUs, when Bsend and Brecv are called in OB1, although the data transmitted consists of only two digital signals, inter-station device interlocking fails to function consistently in practice. When using ABB’s AC800F, if the communication data is defined as global variables, there are no issues when establishing inter-station device interlocks. This indicates that the communication mechanisms and structures of some brands are not yet very reasonable, or rather, their reliability is poor. When used in the process interlocks of critical equipment, it can lead to serious problems and accidents. Of course, when the distance between two stations is not very large, it is more reliable to use additional cables to establish hard interlocks. It would save time and effort if a reliable communication control system could be found.