An assembly has a tachograph and a data memory, in particular a data memory of a data card. The tachograph has an interface designed to exchange data between the tachograph and the data memory, logic function modules and at least one memory. In a method for operating the tachograph, as a result of high security requirements, the data transfer between the data memory and the tachograph is extremely time-intensive. At the start of the data transfer a virtual reproduction of the data memory is created in the memory of the tachograph and the logic function modules first have read and write access to the virtual reproduction in the memory. Data is then regularly written to the data memory of the data card by a write access to the memory, thus eliminating the differences between the virtual reproduction and the data memory.