In 1979 Modicon (now Schneider Electric) defined a serial bus to connect their programmable logic controllers (PLCs) called Modbus. Modbus uses in his first version a two wire cable with EIA 485 with UART signals. The protocol itself is very simple with a master/slave protocol and the number of data types is limited to those understood by PLCs at the time. Nevertheless Modbus is with its Modbus-TCP version still one of the most used industrial network mainly in the building automation field.