Abstract: The disclosure pertains chiefly to an interface including an electrical supply. The disclosure concerns an interface capable of providing an external supply from the amplification of one of the signals. For example, the amplified DTR is used to give a supply voltage to a MIDI interface from an RS 232 serial interface using a nine-pin SUB D9M connector. The disclosure can be applied to the making of interfaces capable of giving an electrical supply to an external device as well as to computers including such interfaces. The disclosure can be applied chiefly to the making of computers capable of working under the MS-DOS operating system and capable of providing a supply voltage to the MIDI interface by means of an RS 232 serial interface and a SUB D9M connector.