Siemens S7 HMI - 300 PLC - 200 PLC MPI Communication
An example of interconnecting a Siemens HMI Touch with an S7 300 PLC and with his elder brother S7 200. Communication is made over MPI at 19.2 KBaud. 300 PLC simply uses SFC67/68 to send data to another MPI node (S7 200 with adress 2), and S7 200 is a PPI master/slave and it is also an MPI slave (receives queries from 300 master).