Re: Unique ID & Acknowledgement in CAN

Hi BoopathiRaja,

1> Refer following application note. Some thing i read when i started with
CAN on AVR.
www.avrfreaks.net/modules/FreaksArticles/files/23/CAN on the AVR.pdf

Only unique CAN Message ID and RTR bit values may be transmitted by any CAN
node. If two or more Tx CAN nodes
using the exact same CAN Message ID and RTR values collide, they will both
pass the priority arbitration together
allowing two or more active CAN nodes to be sending after the arbitration
field. After the arbitration is finished, any
dominant/recessive bit wise difference will cause a CANSTMOB register Tx
BERR (Bit ERRor) in the transmitting CAN
node that sends a recessive bit and sees a dominant bit value instead (two
BERR exceptions have already been noted).
Because CAN has error signaling, error node confinement and automatic
retries of corrupted messages, the BERR will
cause an error flag to be sent over the entire CAN bus (error signaling).
Automatic retries could theoretically create a
situation where the two Tx CAN duplicate Message ID+RTR nodes keep
repeating the same BERR failure over and over,
until the Tx CAN node bus off error handling is triggered by the CANTEC
error counter trying to exceed a value of 255
decimal. The CANTEC error counter is incremented by 8 when sending the
error flag, so if there are no other Tx problems
the 32nd failed BERR retry attempt will cause the bus off (error node
confinement). Since bus off is automatically reset
after receiving 128 occurrences of 11 consecutive recessive bits, the
problems may keep occurring over and over. Just
*remember this problem is caused by the CAN bus designer *using the exact
same Tx CAN Message ID and RTR bit valuesin multiple Tx CAN nodes (it is
not the fault of the CAN system). Of course the exact same Rx CAN Message
ID may be
used in any other CAN node or even in all the other CAN nodes.

2> This the decided at CAN network design level. Those nodes who are
interested for a particular message depending upon your setting in MASK &
filter registers. If received message pass that criteria then automatically
silicon of CAN bus will send ACK in the ACK slot of the CAN bus frame.

It seems you have just started. Just refer wiki for staring point of view.
http://en.wikipedia.org/wiki/CAN_bus

I hope this helps you.

Regards,

Dinesh

On Tue, Feb 5, 2013 at 6:21 PM, PDE-Elect - Software Team 1 <
[email protected]> wrote:

>
> Hi techies,
>
> 1. If i am using same CAN id in 2 different nodes. what will happen.?
> Whether any error will occur or Tx will be in proper..?
>
> 2. How the acknowledgement works in CAN.? How the sender knows the
> acknowledged frame from receiver.?
>
> Regards,
> *
> BoopathiRaja.G *| Product Development Engineering Electronics,
> 0422-4331608 | [email protected]
> *
> Pricol Limited
>
> Website : www.pricol.co.in
> Address : 132, Ooty Main Road, Periyanaikanpalayam, Coimbatore, 641020,
> India.**
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