Signals at point A are acquired by input modules and converted to a digital form. Then they are sent by ET-BUS to output modules located in point B. Output modules have task to convert digital information about input stages and copy these stages to their outputs. There is possibility of two-ways communication. In such case in both A and B points must exist both types of modules: input and output. Modules intercommunicate by ET-BUS interface using dedicated protocol. This protocol assume to connect modules in pairs. Each pair allows transmission of 16 two-stage signals one way. Pair consist of one input and one output module. Both modules must have the same address, which is configured by a user. Pair of modules in ET-BUS network works independently, communicating only within the pair. Information is sent by events. Change of status on the input causes sending a message to the output and change of its status. In other words status of inputs is copied to outputs with the same address. In addition, each module sends every second information about status of its inputs/outputs.
On the ET-BUS could exist only one pair with the same address (one input and one output module). In case of module address duplication the modules will indicate error. It is not possible to send information directly between devices with different address.
In the case, when CPU ET-CU is connected to ET-BUS, it could read input signals status and e.g. send them to present in SCADA system,