GF54.00-P-0005-01A

CAN data bus data telegram

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During normal operation, messages consist of the following transfer frames: Data frame for transmitting CAN messages (such as coolant temperature, etc.). Remote frame for requesting CAN data from a different control unit. Error frame informs all connected control units that an error has occured and that the most recent CAN message is invalid.

The CAN protocol supports two different data frame formats, with the only difference residing in the length of the identifier: - Standard format - Expanded format Only the standard format is currently in use at DaimlerChrysler.

P54.00-1037-09

The data telegram for transmitting CAN messages through the CAN data bus consists of seven sequential blocks: Start of frame: indicates the start of the CAN message (Start bit) and synchronizes all stations. Arbitration field: This field consists of the identifier (identifier and) (address) with 11 bits and one control bit request) (remote transmission request bit). This control bit indicates if the message contains a data frame or a remote frame without bytes. Control field: The control field (6 bits) contains the IDE bit (identifier extension bit) to distinguish (control bits) between the standard and expanded format, a reserved bit for future expansions and the number of bytes contained in the data field in the last 4 bits.

Data field: The data field can contain between 0 and (data) 8 bytes of data. A CAN message with a length of 0 can be employed to synchronize distributed processes. CRC field: The CRC field (cyclic redundancy (check field) check field) consists of 16 bits and is used to detect transmission errors. ACK field: The ACK field (acknowledgment field) (receipt contains a confirmation signal from all confirmation) receivers that have received the CAN message without error. End of frame: Marks the end of the message. (frame end)

Intermission: The interval between two messages. (Intermission) The interval must contain at least 3 bits. The next message can then be sent by any control module.

IDLE: If none of the control modules transfer data, the (idle) CAN data bus remains idle until the next message is sent.