Method and device for serial data transmission having a flexible message size and a variable bit length

A method for serial data transfer, during normal operation of a motor vehicle to transfer data between at least two control units of the motor vehicle that are connected via a data bus in a bus system having at least two bus subscribers that exchange messages via the bus, the method comprising:

• exchanging messages via the bus, transmitted ones of the messages having a logical structure in accordance with the CAN standard ISO 11898-1, the logical structure encompassing a start of frame bit, an arbitration field, a control field, a data field, a CRC field, an acknowledge field, and an end of frame sequence, the control field encompassing a data length code that contains an information item regarding the length of the data field;
• providing, when a first marker (EDL) is present, that the control field of the messages, divergently from the CAN standard ISO 11898-1, encompasses more than six bits;
• implementing the first marker (EDL) by a recessive bit in the control field;
• and
• providing that, when the first marker is present, the recessive bit of the first marker (EDL) is followed, in all data messages, by at least one dominant bit.

A method for serial data transfer, during production or maintenance of a motor vehicle to transfer data between a programming unit connected to a suitable data bus for programming purposes and at least one control unit of the motor vehicle which is connected to the data bus in a bus system having at least two bus subscribers that exchange messages via the bus, the method comprising:

• exchanging messages via the bus, transmitted ones of the messages having a logical structure in accordance with the CAN standard ISO 11898-1, the logical structure encompassing a start of frame bit, an arbitration field, a control field, a data field, a CRC field, an acknowledge field, and an end of frame sequence, the control field encompassing a data length code that contains an information item regarding the length of the data field;
• providing, when a first marker (EDL) is present, that the control field of the messages, divergently from the CAN standard ISO 11898-1, encompasses more than six bits;
• implementing the first marker (EDL) by a recessive bit in the control field;
• and
• providing that, when the first marker is present, the recessive bit of the first marker (EDL) is followed, in all data messages, by at least one dominant bit.