An enclosed needle catheter insertion device includes a catheter assembly and a need insertion device having a needle guard housing to enclose a needle in a shielded position and a needle support supporting the needle for movement between a ready position, with the tip of the needle exposed, to a shielded position with the needle within the needle guard housing. The entire apparatus is arranged overlapping with the output member at a position in an axial direction on a radially inner side of the output member, and a ring gear of the apparatus is integrally provided with the output member, on an inner peripheral surface of the output member. Furthermore, a method is proposed for making possible the bus communications between a control unit as master and at least one connecting element as slave. The information transmitted to the PED may then be displayed, processed, stored or forwarded to another location if needed.