GF54.00-P-0005-01A CAN Data Bus Data Telegram

GF54.00-P-0005-01A CAN Data Bus Data Telegram

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 occurred 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:
- the standard format
- the expanded format

Only the standard format is currently in use at DaimlerChrysler.







The data telegram for transmitting CAN messages through the CAN data bus consists of seven sequential blocks:
- Start of Frame: marks the start of a CAN message
(Start bit) and synchronizes all stations.

- Arbitration Field: This field consists of an identifier
(identifier and ) (address) with 11 bits and a 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: To distinguish between the standard and extended format the Control Field (6 Bit) contains the
(control bits) IDE- bit (Identifier Extension Bit), a reserved bit for future expansions and in the last 4 bits the number of data bytes contained in the data field.

- Data Field: The data field can contain between 0 and 8 Bytes
(data) of data contained. 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) comprises 16 Bit and serves as security for detecting transmission errors.

- ACK Field: The ACK Field (Acknowledgment Field) contains a
(confirmation of confirmation signal from all recipients which
receipt) have received the CAN message free from faults.

- End of Frame: Identifies the end of the data telegram
(frame end)

- Intermission: Interval between two data telegrams The
(interval) interval must contain at least 3 bits. The next message can then be sent by any control unit.

- IDLE: If no control unit transmits, the CAN data bus in idle
(bus idle) condition until the next data telegram is sent.