1. A device for the connection of an apparatus to a signal transmission channel to transmit and receive signals, comprising: a first coupling circuit to electrically couple the device to the signal transmission channel in reception and in transmission; a second circuit electrically coupled to the first coupling circuit, said second circuit to process bits received or sent and to check conformity between the signals received or transmitted with a pre-set standard; and a third circuit electrically coupled to the second circuit and to the apparatus, said third circuit to manage transmitted signals as a function of a use proper to the apparatus; wherein the second circuit comprises a control register corresponding to a type of the signals transmitted or to be transmitted, and a buffer memory to receive the signals transmitted or to be transmitted, said buffer memory electrically coupled to said control register, said control register having a state; the third circuit comprises a microprocessor carrying out, on the signals transmitted or to be transmitted, instructions loaded into a program memory of said microprocessor as a function of the state of said control register; said device comprising, between the second and the third circuit, a fourth interface circuit to match the control protocol specific to a microprocessor of the third circuit with a control protocol of the second circuit, said fourth interface circuit having a multiplexer, said multiplexer programmable by two selection signals sent by said microprocessor of said third circuit.