Raw CAN Receive Messages - Intrepidcs API
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Overview

When neoVI receives a CAN message it assembles the message in a byte sequence. These formats are depicted in tables 1 and 2 below.

 

Table 1 - Standard ID (SID) Frame Format

BYTE 1 BYTE 2 BYTE 3 BYTE 4 BYTE 5 BYTE 6

BYTES 7-14
 NETID_XX

NETID OF CAN NETWORK:

NETID_HSCAN, NETID_MSCAN, NETID_SWCAN, NETID_LSFTCAN

 TIMESTAMP
MSB		 TIMESTAMP LSB STANDARD
ID BITS 10:3
b7 b6 b5 b4 b3 b2 b1 b0
SID Bit2 SID Bit1 SID Bit0 SRR IDE - EID Bit17 EID Bit16
SRR = Set to 1 when a remote frame
IDE = Set to 0 when this is a standard frame.
EID Bit 17 and 16 = undefined  for a standard ID message

 
MS Nibble LS Nibble
Reserved Bits DLC
DLC = Data Length Code

Reserved Bits = Undefined (Mask off to determine length of data)

 

 CAN Data bytes 0 - 8

Remote Frame Have No Data

 

Table 2 - Extended ID (EID) Frame Format

BYTE 1 BYTE 2 BYTE 3 BYTE 4 BYTE 5 BYTE 6 BYTE 7 BYTE 8 BYTE 9-16
 NETID_XX

NETID OF CAN NETWORK:

NETID_HSCAN, NETID_MSCAN, NETID_SWCAN, NETID_LSFTCAN

 TIMESTAMP MSB TIMESTAMP LSB EXTENDED
ID BITS 28:21

 

b7 b6 b5 b4 b3 b2 b1 b0
EID Bit20 EID Bit19 EID Bit18 SRR IDE - EID Bit17 EID Bit16
SRR = Undefined for extended frame
IDE = Set to 1 when this is an extended  frame.
EID Bit 17 and 16 = undefined  for a standard ID message

 

 

 EXTENDED
ID BITS 15:8		 EXTENDED
ID BITS 7:0
MS Nibble LS Nibble
b7 b6 b5 b4
- ERTR Rb1 Rb1
DLC
DLC = Data Length Code

ERTR =Set to 1 when a remote frame

Rb1 and Rb0 = undefined

 CAN Data bytes 0 - 8

Remote Frame Have No Data

 

 

 

C/C++ Examples:

    Getting Standard Frame Arb ID

    uiArbID = (((unsigned int) bPacket[3]) << 3) + ((bPacket[4] & 0xE0) >> 5);

    Getting a Extended Frame Arb ID

uiArbID = ( ((unsigned int) bPacket[3]) << 21) +
        ((((unsigned int)bPacket[4]) & 0xE0) << 13) +
        ((((unsigned int)bPacket[4]) & 0x03) << 16) +
        (((unsigned int)bPacket[5]) << 8) + bPacket[6]; 

Determining if the message is an Extended or Standard ID

        // is this frame a standard or extended frame (Xtd indicated by bit 3 =1)
        if (bPacket[4] & 0x8)
             { // Extended}
         else
            { // Standard}

Determining if the Standard Message is a Remote Frame

// is this frame a remote one (indicated by bit 4)
if (bPacket[4] & 0x10)
    { // Standard ID Remote Frame}
else
    { // Regular Standard Frame }

Determining if the Extended  Message is a Remote Frame

// is this frame a remote one (indicated by bit 6)
if (bPacket[7] & 0x40)
    { // Standard ID Remote Frame}
else
    { // Regular Standard Frame }

Determining Number of Data Bytes for a Standard Frame

        // Mask off upper nibble
        NumberBytesData = bPacket[5] & 0x0F;

Determining Number of Data Bytes for an Extended Frame

        // Mask off upper nibble
        NumberBytesData = bPacket[7] & 0x0F;

 

 

 

intrepidcs API   Documentation - (C) Copyright 2000-2009 Intrepid Control Systems, Inc.

Last Update: Sunday, October 06, 2002