LIBNODAVE, a free communication library for Simatic S7 PLCs :: Linux

LIBNODAVE, a free communication library for Simatic S7 PLCs

The PLCs of the S7-300 and S7-400 family have a so called MPI (multipoint) interface. This interface is mainly used to program the device, but can also be used to read and write data from and to the PLC. The physical layer of the MPI interface is a two wire line operated with differential voltage like RS422 or RS485. [...]You will allways need an adapter from Siemens or another vendor. These adapters are "intelligent" devices built around some microprocessor. They talk MPI to the PLC and something else to your PC. The rest of this document is about this "something else".