Read SAE J1939 protocol data stream

	 Use SAE J1939 Agreed vehicle , Mostly broadcast messages . Set baud rate and filter at the test equipment end ID, receive data , And in accordance with the SAE J1939-71 analysis .
	SAE J1939 Agreement message CAN-ID by 29 position , Its composition is shown in the figure below ：

Receive message items as needed , Set the filter ID Or receive all . according to SAE J1939-21, The data segment range is 0-1785 byte , That is, message broadcasting is divided into single frame and multi frame . Here's an example .

	1、 A single frame 
	 If the engine speed message is received , Reference resources SAE J1939-71, Its PGN by 0xF004(61444), The data length is 8 byte , A single frame can be transmitted .

Filter ID Can be set to 0x00F00400, Mask set to 0x00FFFF00.
Read to data ：0CF00400 70 7D 84 E0 15 00 F3 84
The engine speed is 4、5 Two bytes E0 15( The high byte of data is after ), According to the engine speed SPN（190） Calculate the speed ：

0x15E0=5600;5600*0.125=700(rpm)

	2、 Multiframe 
	 Such as idle torque reference message , Reference resources SAE J1939-71, Its PGN by 0xFEE1(65249), The data length is 19 byte , It needs to be split into multiple frames for transmission .

Read to data ：18ECFF0F 20 13 00 03 FF E1 FE 00
PF=0xEC,PS=0xFF, Manage connections for transport protocols , For transmission 9 Message broadcast of bytes or more ;

data ,BYTE1=0x20, Indicates broadcast announcement information ;
2、3 byte ( The high byte of data is after ) Convert to length 0x0013, Indicates that the data length is 19 byte ;
4 byte 0x03, Indicates that the data is divided into 3 package ;
6-8 byte ( The high byte of data is after ) Indicates the of a broadcast message PGN by 0x00FEE1.

Continue to receive the remaining 3 Packet data ：
18EBFF0F 01 14 01 00 19 5C 20 4E
18EBFF0F 02 19 80 25 52 00 32 47
18EBFF0F 03 80 3E E0 01 2E FF FF
among , The first byte of data is serial number ,03 The last two bytes of the serial number FF、FF For filling .
FEE1 The valid data of is 19 bytes ：14 01 00 19 5C 20 4E 19 80 25 52 00 32 47 80 3E E0 01 2E
The idler reference torque is at 17、18 Two bytes E0 01( The high byte of data is after ), According to the idler reference torque SPN 556 The calculated value is ：

0x01E0= 480; 480*1=480(Nm).