CAN bus

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* 11-bit base identifier, common to CAN-2.0A and B.

** All transmitting ECUs must be listening during this field, and MUST cease transmitting if preempted by a dominant signal

* RTR bit. Remote Transmission Requests (recessive) expect a response.

** Much more common are Data Frames (dominant), which carry payloads and expect no response

** Note that Data Frames will win arbitration against Remote Frames having the same ID

** If the subsequent Identifier Extension Bit is recessive, indicating 29-bit identifiers, this bit MUST be recessive, and the true RTR follows the extended identifier

** In this case, this bit is known as the "Substitute Remote Request" (SRR) bit

* IDE bit. Identifier Extension. Recessive if and only if an 18-bit extended identifier is to be provided, in which case:

** 18-bit extended identifier, combining to make a 29-bit arbitrating ID

** Real RTR bit

** A dominant reserved bit (must accept but not transmit recessive)

After the identifier (whether 11-bit or 29-bit) has been transmitted, it is only possible for one ECU to be transmitting in a compliant network (i.e., where all ECUs have distinct IDs). After this point, the two frame formats are unified:

* A dominant reserved bit

* 4-bit DLC. Data Length Code, specifying a number of data bytes 0--8.

** Larger values (9--15) can appear, but are not used in ISO CAN.

* 0--8 byte Data Field (Data Frames only)

* 15-bit CRC

* A recessive reserved bit (CRC delimiter)

* 1-bit ACK slot

* A recessive reserved bit (ACK delimiter)

* 7 recessive reserved bits (Frame delimiter)

CAN bus: Difference between revisions

Dank (talk | contribs)

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 * 11-bit base identifier, common to CAN-2.0A and B.
 ** All transmitting ECUs must be listening during this field, and MUST cease transmitting if preempted by a dominant signal
 * RTR bit. Remote Transmission Requests (recessive) expect a response.
 ** Much more common are Data Frames (dominant), which carry payloads and expect no response
+** Note that Data Frames will win arbitration against Remote Frames having the same ID
+** If the subsequent Identifier Extension Bit is recessive, indicating 29-bit identifiers, this bit MUST be recessive, and the true RTR follows the extended identifier
+** In this case, this bit is known as the "Substitute Remote Request" (SRR) bit
+* IDE bit. Identifier Extension. Recessive if and only if an 18-bit extended identifier is to be provided, in which case:
+** 18-bit extended identifier, combining to make a 29-bit arbitrating ID
+** Real RTR bit
+** A dominant reserved bit (must accept but not transmit recessive)
+After the identifier (whether 11-bit or 29-bit) has been transmitted, it is only possible for one ECU to be transmitting in a compliant network (i.e., where all ECUs have distinct IDs). After this point, the two frame formats are unified:
+* A dominant reserved bit
+* 4-bit DLC. Data Length Code, specifying a number of data bytes 0--8.
+** Larger values (9--15) can appear, but are not used in ISO CAN.
+* 0--8 byte Data Field (Data Frames only)
+* 15-bit CRC
+* A recessive reserved bit (CRC delimiter)
+* 1-bit ACK slot
+* A recessive reserved bit (ACK delimiter)
+* 7 recessive reserved bits (Frame delimiter)