CAN bus

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===CAN IDs===

Lower IDs have priority over higher IDs. While transmitting a message, each ECU must also listen. If it sees a 0 while sending a 1, it must cease to transmit until the current message ends. Logical 0 is the "dominant" signal:

Lower IDs have priority over higher IDs, and form the 11-bit "Arbitration Field" in a CAN frame (there are 2 such fields in an Extended Frame, one of 11 and one of 18 bits, separated by two bits). While transmitting a message, each ECU must also listen. If it sees a 0 while sending a 1, it must cease to transmit until the current message ends. Logical 0 is the "dominant" signal:

* If multiple ECUs are transmitting at the same cycle, all must transmit recessive, or everyone will see dominant

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* Synchronization begins on the first recessive to dominant transition after an idle period ("start bit" of frame)

* Resynchronization occurs on each subsequent recessive to dominant transition

==Frames==

A frame begins with a transition from recessive to dominant, the "start bit". It is followed by:

* 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

CAN bus: Difference between revisions

Dank (talk | contribs)

@@ Line 20: / Line 20: @@
 ===CAN IDs===
-Lower IDs have priority over higher IDs. While transmitting a message, each ECU must also listen. If it sees a 0 while sending a 1, it must cease to transmit until the current message ends. Logical 0 is the "dominant" signal:
+Lower IDs have priority over higher IDs, and form the 11-bit "Arbitration Field" in a CAN frame (there are 2 such fields in an Extended Frame, one of 11 and one of 18 bits, separated by two bits). While transmitting a message, each ECU must also listen. If it sees a 0 while sending a 1, it must cease to transmit until the current message ends. Logical 0 is the "dominant" signal:
 * If multiple ECUs are transmitting at the same cycle, all must transmit recessive, or everyone will see dominant
@@ Line 26: / Line 26: @@
 * Synchronization begins on the first recessive to dominant transition after an idle period ("start bit" of frame)
 * Resynchronization occurs on each subsequent recessive to dominant transition
+==Frames==
+A frame begins with a transition from recessive to dominant, the "start bit". It is followed by:
+* 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