J1939 presentation by Simma Software

1. Understanding SAE J1939 by Simma Simma, Inc.

9. CAN 2.0A Format SOF: Start of frame (start bit) ID: Message identifier (indicates msg priority) RTR: Remote transmission request IDE: Identifier extension bit (2.0A or 2.0B) r0: Reserved bit. Sent as dominant. DLC: Data length code. Valid range 0 – 8. CRC D: CRC delimiter. Marks end of CRC field. ACK S: Used for receiver to ACK msg. Sent as recessive. ACK D: Marks end of ACK field. EOF: End of frame. (stop bit). Sent as 7 recessive bits. INT: Intermission. Sent as 3 recessive bits.

10. CAN 2.0B Format SRR: Substitute request bit. Sent as recessive. This is simply a placeholder bit to ensure compatibility between 2.0A and 2.0B because 2.0A has RTR.

15. CAN ID = 0x1dffffff (1/1101/1111/1...)

17. Bus Arbitration Example RX RX RX 1 1 0 ECU #3 1 0 0 0 1 0 Bus RX 1 0 0 1 0 ECU #2 1 0 0 0 1 0 ECU #1

21. CAN ID Mapping SA PS PF DP EDP P 0 8 16 24 25 28 26 Source address of controller application (CA). SA: PDU specific. Either destination address or group extension. PS: PDU format: < 240, PS is destination address. (PDU1 format) >= 240, PS is group extension. (PDU2 format) PF: Data page. Used to create a second page of PGNs. DP: Extended data page. J1939 devices must set to 0. EDP: Message priority. Must come first. P:

23. Example J1939 PGN 910 Relative, rear axle #2, right Byte 8: 909 Relative, rear axle #2, left Byte 7: 908 Relative, rear axle #1, right Byte 6: 907 Relative, rear axle #1, left Byte 5: 906 Relative, front axle #1, right Byte 4: 905 Relative, front axle #1, left Byte 3: 904 Front axle speed Bytes 1-2: SPN 100 ms TX Rate: 8 Length: 6 (default) Priority: 65215(0xFEBF) PGN: J1939 Wheel Speed Information

24. J1939 Request PGN PGN which is being requested Bytes 1-3: Global or specific Destination: 3 Length: 6 (default) Priority: 59904 (0xEA00) PGN:

30. BAM Message PGN Byte 6-8: Reserved. Filled with 0xFF Byte 5: Number of packets Byte 4: Message size in bytes Bytes 2-3: Fixed at 32 Byte 1: Global Destination: 8 Length: 7 (default) Priority: 60416(0xEC00) PGN: Transport Protocol – Connection Management

31. Data Transfer PGN Data. Any unused locations in last packet should be filled with 0xFF Bytes 2-8: Sequence number (1 to 255) Byte 1: Global Destination: 8 Length: 7 (default) Priority: 60160(0xEB00) PGN: Transport Protocol – Data Transfer

34. CM Example

35. RTS Message PGN Byte 5-7: Total number of packet sent in response to CTS. Byte 4: Number of packets Byte 3: Message size in bytes Bytes 1-2: Fixed at 16 Byte 0: Specific Destination: 8 Length: 7 (default) Priority: 60416(0xEC00) PGN: Transport Protocol – Connection Management

36. CTS Message PGN Bytes 5-7: Reserved. Filled with 0xFF Bytes 3-4: Next sequence number to start with Byte 2: Max number of packets that can be sent at once. (Not larger than byte 5 of RTS) Byte 1: Fixed at 17 Byte 0: Specific Destination: 8 Length: 7 (default) Priority: 60416(0xEC00) PGN: Transport Protocol – Connection Management

37. End of Msg ACK Message PGN Bytes 5-7: Reserved. Filled with 0xFF Byte 4: Total number of packets. Byte 3: Total message size in bytes. Bytes 1-2: Fixed at 19 Byte 0: Specific Destination: 8 Length: 7 (default) Priority: 60416(0xEC00) PGN: Transport Protocol – Connection Management

38. Connection Abort Message PGN Bytes 5-7: Reserved. Filled with 0xFF. Bytes 2-4: Connection abort reason. Byte 1: Fixed at 255 Byte 0: Specific Destination: 8 Length: 7 (default) Priority: 60416(0xEC00) PGN: Transport Protocol – Connection Management

40. J1939 Address Claimed PGN NAME field Byte 1-8: SA requested (254 for Cannot Claim) Source: 8 Length: 6 (default) Priority: 60928(0xEE00) PGN: