The device described is used to convert a diagnostic interface to standard SPI and includes: an electronic unit (10), having a data input (14), a data output (17), a synchronization input (15), a clock input (16) and a register (13) and a buffer unit (12), having a signal input (19), a signal output (20) and an activation input (21). The data input (14) and the data output (17) of the electronic unit (10) are connected to each other by a first data line (18). The data output (17) for the electronic unit (10) is connected to the signal input (19) on the buffer unit (12) by a second data line (22).