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Can Protocol with Single Node

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jagdish27

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Hi,

I am new to CAN protocol, going through the Robert Bosch's CAN Specification ver2.0 Part B. I can't understand the following lines on page 63

" Note:

Start up / Wake up:

if during startup only one node is online, and if this node transmits some message, it will get no acknowledgement, detect an error and repeats the message. It can become 'error passive' but not 'bus off' due to this reason."

As far as I understand when a transmitter detects an error(like Acknowledgement error) it retransmits the message and also increments the transmit error count (TEC) by 8. So if there is only one node then its TEC should increase by 8 everytime it transmits a message and should go into 'bus off' condition once TEC goes above 255.

Can someone please explain why the specification says it can only go 'Error Passive' but not 'Bus off'?.

Thanks in Advance,

Jagdish.
 
I'm only just starting out with CAN as well so don't take my word for gospel, but have a look at section 3 exception 1.

In error passive mode, it doesn't increment TEC for ACK errors unless it also detects a dominant state on the bus during its error frame (being in error passive its error frame is 6 recessive bits, a dominant bit would indicate another node is active).
 
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