A data processing and transmission system (1) for a numerical control unit (2) adapted to control a machine tool (3), comprises at least one input channel (4) adapted to a transit of operational signals from or to devices present in the machine tool, electronic circuits configured to process the operational signals to make available on an output interface (5) control signals for the numerical control unit, a multipolar cable (8) having a first and a second end, each provided with a multipolar connector (9), a master unit having the output interface, a main processor, a memory and at least one socket (7A) configured to be coupled to one of the multipolar connectors, one or more slave units (6), each provided with at least one external port (6A) defining the input channel, a memory, a secondary processor, and provided also with a first socket (6B) and a second socket (6C), configured to be coupled at least to a first or a second connector of the multipolar connectors in order to interconnect the slave unit at least with the master unit. The master unit has a clock and each slave unit has its own clock. The main processor of the master unit generates a synchronization signal and transmits it through the multipolar cable in order to synchronize all the clocks of the slave units with the clock of the master unit.