Apparatus for manipulating interface signals, having • a slave interface which can be connected to a master interface of a control device, • a master interface which can be connected to a slave interface of a measuring device, • a circuit arrangement which is supplied with at least one data input signal (DIN_S, DIN_M) for each interface (12, 18) and outputs a corresponding data output signal (DOUT_M, DOUT_S) for each data input signal (DIN_S, DIN_M) to the respective other interface (12, 18), characterized in that the circuit arrangement a) comprises at least one manipulation unit (110, 120), which is supplied with a data input signal (DIN_S, DIN_M) and a substitute data signal (DE_S, DE_M) and outputs a corresponding data output signal (DOUT_M, DOUT_S), b) and a protocol unit which is supplied with at least one protocol-relevant interface signal (DIN_S, DIN_M, TCLK_S) and uses manipulation rules and information received with the at least one protocol-relevant interface signal (DIN_S, DIN_M, TCLK_S) to select when the at least one manipulation unit (110, 120) outputs the corresponding data input signal (DIN_S, DIN_M) or the substitute data signal (DE_S, DE_M) as the data output signal (DOUT_M, DOUT_S), and c) wherein the substitute data signal (DE_S, DE_M) is generated by the protocol unit using the manipulation rules. • a slave interface which can be connected to a master interface of a control device, • a master interface which can be connected to a slave interface of a measuring device, • a circuit arrangement which is supplied with at least one data input signal (DIN_S, DIN_M) for each interface (12, 18) and outputs a corresponding data output signal (DOUT_M, DOUT_S) for each data input signal (DIN_S, DIN_M) to the respective other interface (12, 18), characterized in that the circuit arrangement a) comprises at least one manipulation unit (110, 120), which is supplied with a data input signal (DIN_S, DIN_M) and a substitute data signal (DE_S, DE_M) and outputs a corresponding data output signal (DOUT_M, DOUT_S), b) and a protocol unit which is supplied with at least one protocol-relevant interface signal (DIN_S, DIN_M, TCLK_S) and uses manipulation rules and information received with the at least one protocol-relevant interface signal (DIN_S, DIN_M, TCLK_S) to select when the at least one manipulation unit (110, 120) outputs the corresponding data input signal (DIN_S, DIN_M) or the substitute data signal (DE_S, DE_M) as the data output signal (DOUT_M, DOUT_S), and c) wherein the substitute data signal (DE_S, DE_M) is generated by the protocol unit using the manipulation rules. a) comprises at least one manipulation unit (110, 120), which is supplied with a data input signal (DIN_S, DIN_M) and a substitute data signal (DE_S, DE_M) and outputs a corresponding data output signal (DOUT_M, DOUT_S), b) and a protocol unit which is supplied with at least one protocol-relevant interface signal (DIN_S, DIN_M, TCLK_S) and uses manipulation rules and information received with the at least one protocol-relevant interface signal (DIN_S, DIN_M, TCLK_S) to select when the at least one manipulation unit (110, 120) outputs the corresponding data input signal (DIN_S, DIN_M) or the substitute data signal (DE_S, DE_M) as the data output signal (DOUT_M, DOUT_S), and c) wherein the substitute data signal (DE_S, DE_M) is generated by the protocol unit using the manipulation rules.