HI all, I dont know whether to post this question in this group.If this question doesn't belongs to this group please ignoe this.Can any body know why the names CANH and CANL got its names in the Control area network which is a serial communication protocol that was developed by Bosch.And also how the dominant and Recessive got its names.
With Regards, Sudheervemana
I'm just guessing here but I assume L and H in CANL, CANH stand for low and high. eg in the differential bus a dominant signal raises the CANH line and lowers the CANL line.
The dominant state can override the recessive state, hence the names.
-Daniel
Correct. Can is a differential based system. You need to maintain polarity through the system, thus the designations, RS-485A and RS-485B.
As a note, CAN can function on only one of those signals if ground is properly maintained.
For noise immunity, CAN uses a differential pair of wires to transmit the data signal. Bosch publishes the specs for the PHY layer. As for the data encoding, it's a distributed bus that anyone can transmit on at any time. The beginning of the packet encodes the CAN identifier of the sender where lower numbers take precedence over higher ones. That way if two nodes start transmitting frames at exactly the same time, the higher one can sense that its assertion of a recessive bit doesn't match the current bus state (dominant), flipping it immediately into receive mode and delaying the Tx. There are no collisions on CAN, unlike Ethernet.
In my last job, I wrote a lot of firmware to move CAN data between mass flow controllers on semiconductor tools, including debugging the physical layer issues. Email me if you need more help.
Dan
sudheervemana wrote:
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