In the case of an ET-208 or ET/MT-3x6 with RS 442 interface, a connection to an MPI bus is established via the HMI-RS422 MPI box. Its main purpose is to adapt the RS 422 interface to the RS 485 bus system of the MPI interface. In the transport layer (layer 4), the MPI box uses the RK512 protocol, and at the connection level it uses the 3964/R procedure. For further information, for example on the parameterisation of the MPI box, please refer to the MPI box manual.
Connection of ET-2x8 or ET/MT-3x6 devices to the CPU 3xx and CPU 4xx PLCs by Siemens.