How to read a particular arbitration id from CAN bus

[R_J]

Hi All,

I want to read a CAN message with arbitration id 700h from CAN bus. There may be more then one CAN message available on the bus. How can i read a CAN message of particular arbitration id from CAN bus.

Kindly reply as soon as available.

Regards,

J 

[Shreyas]

Hi ,

     Check out the following VI. Also refer to the CAN manual: http://www.ni.com/pdf/manuals/370289m.pdf

Hope that helps.

Kudos are welcome.

[R_J]

Hi,

Kindly attached this example in Labview 7.1.

[Shreyas]

Hi,

    I am attaching the screenshot of the VI. Hope it works in 7.1. Else upgrade LabVIEW.

Kudos are welcome

[R_J]

Hi All

With ncOpen.vi we can set the particular arbitration id that we want to read from the CAN bus. Now if i have to read 3 arbitration id & write 2 arbitration id then can it possible by using one ncOpen.vi function or i have to use ncOpen.vi for every arbitration id ?

Kindly reply as soon as possible.

/J

[R_J]

Also let me know what is the use of Mask & Comparator in ncConfigCANNET.vi.  Can it be use for filtering the Arbitration id which we want to read ?

[Shreyas]

Hi,

  With ncopen you can only set one arbitration id. Check out the ncreadobjmulti.vi and ncwritemultiobj.vi 

Examples of CAN in Example finder will help you understand it better.

 Standard Comparator is the CAN arbitration ID for the standard (11-bit) frame comparator.

Standard Mask is the bit mask used in conjunction with the Standard Comparator attribute for filtration of incoming standard (11-bit) CAN frames. If the mask/comparator matches, the frame is stored in the Network Interface queue, otherwise it is discarded. Bits in the mask that are clear are treated as don't-cares. For example, hex 00000700 means to compare only the three upper bits of the 11-bit standard ID.

Kindly refer to the following threads and manual for more information:

http://www.ni.com/pdf/manuals/370289k.pdf

http://forums.ni.com/ni/board/message?board.id=30&message.id=505&requireLogin=False

http://forums.ni.com/ni/board/message?board.id=30&requireLogin=False&thread.id=2010

Message Edited by Shreyas on 09-03-2009 12:16 PM

[R_J]

Hi

Thank you very much for the useful reply.

If i want to read 800h to 805h arbitration id then what will be the Standard Comparator & Standard Mask value ?

Thanxs in advance

[R_J]

i am using PCI-CAN/XS series card with labview 7.1

[Shreyas]

The comparators and masks are used to filter which frames are received by the Network Interface Object. Standard and extended refer to the CAN arbitration ID where standard is 11 bits and extended is 29 bits. How you set the comparator dictates which frames will be received.

As an example, consider a CAN network receiving 3 IDs (01, 02, and 03, see the readmultnet.vi example). The combination of the comparator and the mask will determine which frames are received. The tables below describe this behavior (note all values are in Binary).

The Mask is the bitmask used in conjunction with NC_ATTR_CAN_COMP_STD for filtration of incoming standard CAN frames. For each bit set in the mask, NI-CAN checks the corresponding bit in the standard frame comparator for a match. Bits in the mask that are clear (i.e., set to 0) are treated as "don’t cares". For example, hex 000007FF (in the comparator) means to compare all 11 bits of incoming standard CAN frames.

Note:

1. If you intend to use CAN Objects as the sole means of receiving standard CAN frames from the network, then you should disable all standard frame reception in the CAN Network Interface Object by setting the Standard Comparator Attribute to NC_CAN_ARBID_NONE (CFFFFFFF hex). Hence, if the standard frame comparator is NC_CAN_ARBID_NONE (0xCFFFFFFF), then NI-CAN ignores the mask, and all standard frame reception is disabled in the CAN Network Interface Object.
   
2. If you intend to use the Network Interface as the sole means of receiving standard CAN frames from the network, then you should set the Standard Comparator Attribute of the Network Interface Object to 0.

Comparator           11           11                 11              11
Mask                 00           01                 10              11
Frames Received     All      01 (1), 11 (3)     10 (2), 11 (3)     11 (3)
	
	 
Comparator           00           00                 00              00
Mask                 00           01                 10              11
Frames Received     All         10 (2)             01 (1)           None

Extended comparators and masks work in exactly the same way. As you can see, it is possible to use complex combinations of these attributes to precisely define which frames will be received.

Also suggest you to go through the CAN manual and labview help and check out this forum: http://forums.ni.com/ni/board/message?board.id=30&message.id=2209&requireLogin=False

Kudos are welcome