j1939

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  1. N

    Why J1939 XBR message checksum needs to be right shifted by 4 bit and added to the checksum ?

    Attached is External Brake Request(XBR) J1939 message checksum calculation. SAE J1939 Digital Annex(DA) specifies this checksum algorithm. The result of the calculation is 4-bit checksum. Why is checksum right shifted by 4 bits and added to checksum? Why not just take 4 least significant...
  2. M

    Trigger power to my Dashcam ignition wire based on vehicle Ignition from CAN high Pin on the j1939 port.

    I want to Trigger power to my Dashcam ignition wire based on vehicle Ignition from CAN high Pin on the j1939 port. I have attempted to use this module: https://pac-audio.com/products/tr-4?_pos=2&_sid=b059f84a1&_ss=r to detect voltage on the CAN high pin but the output voltage seems to bounce...
  3. N

    Why message cannot be found in CAN database (.dbc text file) ?

    I have CAN database (dbc file). It's a text file. The extension of this file is dbc. When it is opened in Vector CANdb++ Editor, J1939 messages and CAN IDs are populated. However, some of the CAN IDs that are in the CANdb++ Editor could not be found in the .dbc text file, I open the .dbc...
  4. N

    Please explain AIR1 standard SAE J1939 message.

    Consider a truck. The Electronic Brake Systems (EBS) ECU receives following message from some other ECU. Please explain this message. From where does some other module acquire the Suspect Parameters Number (SPNs) to send to EBS ECU. What does EBS do with the SPNs it receives?
  5. N

    Can CAN 2.0B and J1939 coexist in the same CAN Network?

    Please consider CAN communication network in a heavy vehicle: Steering Electronic Control Unit (ECU) has CAN 2.0B. It doesn't have J1939 stack. All other ECUs in this network are implemented with J1939 stack. Can CAN 2.0B coexist with J1939? What code changes are needed in steering ECU and...
  6. N

    What are comprehensive differences between J1939/Extended CAN vs. J1939/CAN FD?

    How does messaging work in CAN FD? How are PGNs and SPNs defined for CAN FD? For Extended CAN, SAE J1939-71 defines PGNs and SPNs. All the PGNs and SPNs defined in SAE J1939-71 don't apply to CAN FD? For example, in SAE J1939-71 PGN 65267 is Vehicle Position. There are two SPN's in this...
  7. N

    What are some failure modes and causes and effects of these failures for communication of fault information on J1939 network?

    Please consider Electro Hydraulic Power Steering (EHPS) System installed in a commercial truck. It has dual motors and dual pumps and dual pump Electronic Control Units (ECUs). These pump ECUs communicate with other ECU over public J1939 network. Embedded steering software executes in pump...
  8. SaMirakle

    Need Help Decoding Automotive CAN Bus Extended Frame Bits

    Hi everyone, I don't know why but I'm having a tough time decoding CAN Bus data frames, even after looking at many sources showing bit field diagrams of how the data is supposed to be structured. Background on project/goal My main goal is to connect directly to an electronic turbo actuator...
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