[UDS unified diagnostic service] II. Network layer protocol (2) - data transmission rules (single frame and multi frame)

Two 、 Network layer protocol （2）— Data transmission rules （ Single frame and multi frame ）

1. Single frame data transmission rules

2. Multi frame data transmission rules

（1） Achieve the goal ：

（2） Detailed transmission process ：

（3） Detailed meaning analysis of transmitted byte data ：

3. Network layer timing and error handling （ Take multi frame transmission as an example ）

notes ： The picture below needs some effort , Understand and understand the meaning of each time representative in detail

4. Some instructions

（1） Consecutive frames SN（Sequence Number） Add rules

• Consecutive frames :
  Consecutive frames appear after the first frame ,PCI The upper half byte of is 0010b, The lower half byte indicates the sequence number of consecutive frames (SN) .

• SN The value of is defined according to the following provisions :

  • The first frame of a continuous frame SN The value is 1; Every successive frame added ,SN Increase in value 1;
  • The flow control frame does not affect SN The calculation of the value ;
  • When SN Its value 15 after , Of the next consecutive frame SN The value is 0.

• Serial number （SN） Definition :
  

（2） Diagnostic message format ：

• SF_DL: Single frame data length （4Bit）
• FF_DL: Continuous frame data length （12Bit）
• SN: Sequence Number, Serial number of consecutive frames （4Bit）
• FS: Flow State, Flow control state
• BS: Block Size, Allow one continuous transmission CF The number of
• STmin: Two CF Minimum interval between sending , Unit is ms
• N/A: Not Applicable, Don't use