The format of the transmission of isochronous data packets via the IEEE 1394 bus is defined in the IEC 61883 Standard. A bus packet used to transmit the data has a header (1394H) at the beginning, which header describes the format of the bus packet. This is then followed by an isochronous data format header (CIPH), which defines the data format of the useful data in the useful packet. The invention is concerned with the problem of compiling a bus packet for transmission via the 1394 bus. In the case of the invention, this is done in such a way that when the isochronous data transmission is set up, the isochronous data format header (CIPH) prescribed by the application is written both to a special register (38) that is provided and to the buffer memory (32) for the bus packets and the useful data are attached thereto. As a result, it is then possible that a data transmitting section (35) has to take the data to be transmitted, including the isochronous data format header (CIPH), only from the buffer memory (32). A multiplex operation joining together the data and the isochronous data format header (CIPH) need not then be effected for the transmission of the data.