j1939

This module holds definitions of J1939 Protocol Data Unit (PDU) frames.

Example of usage:

>>> from canlib import Frame, j1939
>>> from canlib.canlib import MessageFlag
>>> def frame_from_pdu(pdu):
...     can_id = j1939.can_id_from_pdu(pdu)
...     frame = Frame(
...         id_=can_id,
...         data=pdu.data,
...         flags=MessageFlag.EXT,
...     )
...     return frame
>>> pdu = j1939.Pdu1(
...     p=3, edp=0, dp=0, pf=0x99, ps=0xfe, sa=0xfe,
...     data=[1]
... )
>>> frame_from_pdu(pdu)
Frame(id=211418878, data=bytearray(b'\x01'), dlc=1, flags=<MessageFlag.EXT: 4>, timestamp=None)

The particular characteristics of J1939 are:

• Extended CAN identifier (29 bit)

• Bit rate 250 kbit/s

• Peer-to-peer and broadcast communication

• Transport protocols for up to 1785 data bytes

• Network management

• Definition of parameter groups for commercial vehicles and others

• Manufacturer specific parameter groups are supported

• Diagnostics features

(Extended) Data Page Bit

Extended Data page	Data page	Description
0	0	SAE J1939 Page 0 Parameter Groups
0	1	SAE J1939 Page 1 Parameter Groups (NMEA2000)
1	1	SAE J1939 reserved
1	1	ISO 15765-3 defined

New in version 1.18.

Protocol Data Units

class canlib.j1939.Pdu(*, p: int, edp: int, dp: int, pf: int, ps: int, sa: int, data: List[int] = None)

Protocol Data Unit in j1939.

Base class with attributes common to Pdu1 and Pdu2

data: Optional[List[int]]

data field

dp: int

data page

edp: int

extended data page

p: int

priority

pf: int

PDU format

ps: int

PDU specific

sa: int

source address

class canlib.j1939.Pdu1(*, p: int, edp: int, dp: int, pf: int, ps: int, sa: int, data: List[int] = None, da: int = None, pgn: int = None)

Protocol Data Unit, Format 1

When Pdu.pf < 240, the PDU Specific field is a Destination Address and

pgn = Extended Data Page + Data Page + PDU Format + “00”

da: Optional[int]

destination address, Pdu.ps

pgn: Optional[int]

parameter group number

class canlib.j1939.Pdu2(*, p: int, edp: int, dp: int, pf: int, ps: int, sa: int, data: List[int] = None, ge: int = None, pgn: int = None)

Protocol Data Unit, Format 2

When Pdu.pf >= 240, the PDU Specific field is the Group Extension

pgn = Extended Data Page + Data Page + PDU Format + Group Extension

ge: Optional[int]

group extension, equal to Pdu.ps

pgn: Optional[int]

parameter group number

Converting CAN Id

For a j1939 message, the CAN identifier is divided into the following fields:

Priority	Extended Data Page	Data Page	PDU Format	PDU Specific	Source Address
3 bit	1 bit	1 bit	8 bit	8 bit	8 bit

Use pdu_from_can_id and can_id_from_pdu to convert.

canlib.j1939.pdu_from_can_id(can_id)

Create j1939 Protocol Data Unit object based on CAN Id.

Parameters

can_id (int) – CAN Identifier

Returns

Pdu1 or Pdu2 depending on value of can_id

canlib.j1939.can_id_from_pdu(pdu)

Extract CAN Id based on j1939 Protocol Data Unit object.

Parameters

pdu (Pdu1 or Pdu2) – Protocol Data Unit

Returns

can_id (int) – CAN Identifier