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  1. #1
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    Which parameter decided communication limit of any protocol?

    Hello,
    Can anyone tell me, on physical level as well software/application level, which parameter decided speed limit of communication channel/protocol?
    Example I always hear, LIN will go up to 20Kbps only, why not 10Mbps?
    CAN can go up to 5Mbps only, why not 50Mbps?

    What is limiting these communication protocols?

    •   Alt27th December 2016, 11:53

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    Re: Which parameter decided communication limit of any protocol?

    Hi,

    Usally those communication work with a fixed baud rate, this limits the overall bits/s to be transferred.
    Then there are start bits, stop bits, frame sync bytes, dedicated times of no data transfer, header bytes, error detection bytes, address bytes and so on...
    Some are half duplex only..
    This all decreases the payload.

    Now you may say: why not simply use a higher baud rate?
    But this depends on a lot of parameters:
    * microcontroller/processor hardware.
    * reaction time
    * length of bus
    * type if wires/signalling
    * expected noise level
    * power requirements
    * and a lot more

    *****
    You really may compare it with human communication.
    * it is simple to listen to a fairy tale in a quit room (even if spoken very fast)
    But it's more difficult
    * with noise of machines around
    * with other talking people around
    * if it's a difficult technical topic
    * if it's foreign language and you have to translate it (mentally)
    * or if there is an interpreter
    * or you not only have to listen, but to answer, too
    * or you have to write it down
    * and a lot other influences...

    Klaus


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    •   Alt27th December 2016, 12:25

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    Re: Which parameter decided communication limit of any protocol?

    Hi, Thanks for your valuable thoughts! I appreciate.
    But imagine you have very high end micro-controller ( Multi-core) and its automotive application so no power limitation since it comes from battery.
    Also if I am talking about two CPUs talking to each other.
    Then why this limitation is there? If I want to send data to other micro-controller very fast & with less latency, CAN might be good.
    But it is offering less bandwidth.
    So I did not understand why CAN can not support high data transfer.
    What was limiting factor.

    If you say ECU to ECU transfer, I agree to noise environment.
    That is perfect co-relation.



    •   Alt27th December 2016, 13:08

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    Re: Which parameter decided communication limit of any protocol?

    Hi,

    ..simply because you are talking only of "high performance microcontroller" communication.

    But CAN was developed for many low performance sensors on a bus.
    A water temperature sensor maybe just needs to send the temperature value once per minute.
    And the bus speed and protocol needs to comply with ALL sensors.

    If you want to transmit high volume data peer to peer, then CAN most likely is not the best protocol/hardware.

    --> choose an appropriate hardware and protocol.

    Klaus



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    Re: Which parameter decided communication limit of any protocol?

    CAN can go up to 5Mbps only, why not 50Mbps?
    Where do you see 5 Mbit/s in CAN specification?



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