Is the filter for CAN messages before or after the receiver / ack hardware?
Consider only two nodes on a bus, the first node has ALL messages filtered out, the second node transmits a message that will be filtered by the first node. Will the first node still generate the ACK on the bus, assuming no errors in the packet?
Does the ACK occur before or after the filter is applied?
Please provide sources for your information / opinion.
thanks
On 17 Feb 2006 14:09:11 -0800, snipped-for-privacy@yahoo.com wrote in comp.arch.embedded:
ACK is always sent by all enabled nodes receiving a valid packer that are not the transmitter of the packet. Filtering only determines whether or not the received message gets stored in a mailbox, and for controllers with multiple filters, which mailbox.
Filtering comes after the ACK is sent.
Yes.
The whole point of the Ack mechanism is letting the transmitter know that is connected to a valid network.
A CAN bus device is broadcasting all kinds of information someone _might_ be interested in. If the other stations would just acknowledge those messages they are interested in, it might take a while, before the transmitter would detect that it is not connected to a network.
You may also have to set the acceptance filter much wider and do the final filtering in the software, the Ack mechanism would still not be an indication that someone is actually interested in your message.
Paul
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