Data Link Layers

1
In-Vehicle Networking for Heavy Duty
SystemsReview of CAN / SAE J1939/ ISO 11783

• Data Link Layers
• ISO 11783 Part 3
• J1939-21

2
A look at Architecture
FAQ

• Any information on the number of layers
  associated with it would be very useful.
  Hardware layers, software layers etc. This will
  help us figure out how sophisticated we have to
  get initially. We may not need to implement all
  of the architecture.

3
ISO 11783/J1939 communications system
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ISO 11783 Data Link Layer - General

• Based on CAN 2.0b 29 bit identifiers
• Defines the identifier meaning
• Physical Addressing ( 256 addresses)
• Independent priority field
• Data content identifier independent of sender
• Two message structures
• Type 1 - Destination Specific - both source and
  destination
• Type 2 - Extended - Only source address
• Defines requests and acknowledgement
• Defines proprietary message structure
• Includes a Transport Protocol with two modes
• Managed Connection
• BAM

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Message Capabilities

• Two identifier types (PDUs)
• ECU to ECU
• ECU to All

TYPE
PDU 1
Source Address
Destination Addr
Parameter Group
P
P
P
R
G
Parameter Group
PDU 2
-- PDU Format --
Group Extension -
P
P
P
R
G
Source Address
Priority
First 8 Bits
Reserved
Between 240 and
Page Bit
255
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Identifier Structure
PDU2
Priority
PDU1
8670 Parameter Groups can be defined 480 PDU1,
8190 PDU2
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PGN - Parameter Group Number
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Message Capabilities
Global
9
Message Capabilities
10
Message Capabilities
Not in 11783
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Message Capabilities
12
Replys to Requests
13
Message Capabilities
14
(No Transcript)
15
Message Capabilities
16
Message Capabilities
200 ms between data packets!
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Design Recommendations

• REQUEST SCHEDULING
• The scheduling of a request should be canceled
  if information requested is received prior to
  request being sent. Parameter Groups should not
  be requested if they are recommended to be
  broadcast.

18
Design Recommendations

• DEVICE RESPONSE TIME AND TIME-OUT DEFAULTS
• All devices, when required to provide a response,
  must do so within 0.20 s. All devices expecting
  a response must wait at least 1.25 s before
  giving up or retrying.

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Design Recommendations

• REQUIRED RESPONSES
• A response is required for a global request from
  all devices that have the requested PG, even the
  requester. Acknowledgments are not allowed for
  global requests. There is no restriction on
  minimum response time!

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Design Recommendations

• CTS NUMBER OF PACKET RECOMMENDATION
• During normal vehicle operation it is recommended
  that the maximum number of packets that can be
  sent per CTS be set to 16.