Automotive and Embedded Networks
CAN Protocol
Solved!
@RamNarwade wrote:
i have a doubt Is it possible for a CAN node transmit message and receive the same message after some time. is it possible to do so?
Of course. It probably isn't a very good design but there is no functional reason this can't be done. Typically a specific CAN ID is designated to a piece of hardware. This means that one device is usually responsible for sending an ID. This way any device on the bus that sees this ID knows that this device is there and sent it. If one device receives that ID, and also sends that ID, then a 3rd device on the bus will see both of those messages and won't be able to distinguish which device sent it by the ID alone. You could put some kind of identifier in the payload to help figure out where it originated from.
@RamNarwade wrote:
Thank you for your response and very good explanation. coming back to the same question, inside DBC I cant add same Message id in Rx messages and Tx Messages, is it because some functional limitations or it is just because DBC is made accordingly such that node should not have same Message id in Rx messages and Tx Messages? Thanks in advance!
Lets pretend I have phone at home, but I'm really cheap. And instead of answering the phone and being charged with the minutes, I tell a friend of mine to call me, and let it ring once then hang up. I tell this friend that if he does this I know he is wants me to come over. If he lets the phone ring twice and hangs up then that means he is coming over. If I get a second friend and we want to have the same arrangement then I hope it is clear to you that we can't just let the phone ring once or twice, because those signals have already been used. If I tell the second friend to let the phone ring once then I won't have a way of knowing which friend is calling, or what they want. Maybe the second friend calling and ringing once means he his coming over, or does it mean he wants me to come over? Or it could mean something all together.
The DBC file is the translator. It tells me how many rings, means what, and who it is from. There isn't anything stopping my phone from ringing any number of times, from any caller (just like CAN anyone can use any ID) but be aware that by doing that you lose the ability to know who called and for what purpose. Since the purpose of the DBC is to define what the rings (IDs) mean, it doesn't make sense to have two entries for the same ID. Now if I do answer the phone I can listen to the voice (payload) then I might be able to determine who it is and what they want. But at that point I'm no longer dealing with the translator, and instead are dealing with the raw data (frame).
