The invention relates to a method for exchanging data between a tachograph (DTCO) and a terminal device (CALTEST). The data transmission protocol provides for the terminal device (CALTEST) to cause the tachograph (DTCO) to perform a service by indicating at least one service identification (SID). The aim of the invention is to further develop a method for transmitting data in such a way that a flexible compatibility of the tachograph is obtained. Said aim is achieved by the fact that the tachograph (DTCO) encompasses an allocation of internal service identifications (IIDS) to external service identifications (EIDS), said external service identifications (EIDS) are used during data exchange with the terminal device (CALTEST), and external service identifications (EIDS) of incoming data are exchanged with matching internal service identifications (IIDS) according to the allocation (mapping list MAP) by means of a communication module (COMM).