Plug connector modular system having the following: a. a modular frame for a rectangular plug connector, wherein the modular frame has two long side parts (221, 222) opposite one another; b. a bus system having at least one data bus, having at least one conductor track for electronic data transmission that extends over at least one of the two long side parts in the longitudinal direction; c. a master module which is arranged or can be arranged in the modular frame and has at least one electrical bus contact for transmitting requests and for receiving responses via the data bus; d. a plurality of slave modules (4, 5, 6) which are arranged or can be arranged in the modular frame and each have at least one electrical bus contact (43, 53, 63) for receiving requests from the master module and for transmitting responses to the master module; characterized in that e. the master module and the slave modules (4, 5, 6) are connected to one another in an electrically conductive manner in the form of a parallel circuit by way of their respective at least one bus contact (43, 53, 63) via' the at least one conductor track, wherein at the same time f. the slave modules (4, 5, 6) are connected to the master module via the data bus by way of a data transmission structure in the form of a star point, wherein the master module forms the star point, wherein g. said conductor tracks (14, 14', 14", 14′′′, 14ʺʺ) are integrated in at least one circuit board, and wherein the at least one circuit board is fitted in or on one of the two or in or on both long side parts within the modular frame, and wherein each of said conductor tracks (14, 14', 14", 14′′′, 14ʺʺ) respectively has at least one contact pad (131, 131', 132, 132', 133, 133', 134, 135, 136) and/or one contacting region for the purpose of making contact with the bus contacts (33, 33', 43, 53, 63) of both the slave modules (4, 5, 6) and the master module. a. a modular frame for a rectangular plug connector, wherein the modular frame has two long side parts (221, 222) opposite one another; b. a bus system having at least one data bus, having at least one conductor track for electronic data transmission that extends over at least one of the two long side parts in the longitudinal direction; c. a master module which is arranged or can be arranged in the modular frame and has at least one electrical bus contact for transmitting requests and for receiving responses via the data bus; d. a plurality of slave modules (4, 5, 6) which are arranged or can be arranged in the modular frame and each have at least one electrical bus contact (43, 53, 63) for receiving requests from the master module and for transmitting responses to the master module; e. the master module and the slave modules (4, 5, 6) are connected to one another in an electrically conductive manner in the form of a parallel circuit by way of their respective at least one bus contact (43, 53, 63) via' the at least one conductor track, wherein at the same time f. the slave modules (4, 5, 6) are connected to the master module via the data bus by way of a data transmission structure in the form of a star point, wherein the master module forms the star point, wherein g. said conductor tracks (14, 14', 14", 14′′′, 14ʺʺ) are integrated in at least one circuit board, and wherein the at least one circuit board is fitted in or on one of the two or in or on both long side parts within the modular frame, and wherein each of said conductor tracks (14, 14', 14", 14′′′, 14ʺʺ) respectively has at least one contact pad (131, 131', 132, 132', 133, 133', 134, 135, 136) and/or one contacting region for the purpose of making contact with the bus contacts (33, 33', 43, 53, 63) of both the slave modules (4, 5, 6) and the master module.