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Thread: What is canbus???

  1. #1
    Regular Member wardy's Avatar
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    Default What is canbus???

    OK, been on here a while know and I keep seeing references to cars being full canbus etc. Being a thicko in all things mechanical what is Canbus?

    I thought you smoked the stuff?

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    Regular Member Orka The Porka's Avatar
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    It's digital data. Basically you used to be able to tap into a speed pulse sense wire and now you can't. It's a pain in the a$$.

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    Regular Member yorkshireborn's Avatar
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    Vehicle : saab 95


    Engine : 2.3t

    Year : 2006

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    to make it simple it means u cant swap and change anything electrical on the car

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    Regular Member RSV_Ecosse's Avatar
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    So whats half canbus?.

    Seen that get mentioned a few times here as well.

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    Regular Member willc01's Avatar
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    CAN Bus Description

    The Controller Area Network (CAN) specification defines the Data Link Layer, ISO 11898 defines the Physical Layer.

    The CAN bus [CANbus] is a Balanced (differential) 2-wire interface running over either a Shielded Twisted Pair (STP), Un-shielded Twisted Pair (UTP), or Ribbon cable. Each node uses a Male 9-pin D connector. The Bit Encoding used is: Non Return to Zero (NRZ) encoding (with bit-stuffing) for data communication on a differential two wire bus. The use of NRZ encoding ensures compact messages with a minimum number of transitions and high resilience to external disturbance.



    A number of different data rates are defined, with 1Mbps (Bits per second) being the top end, and 10kbps the minimum rate. All modules must support 20kbps. Cable length depends on the data rate used. Normally all the devices in a system transfer uniform and fixed bit-rates. The maximum line length is 1Km, 40 meters at 1Mbps. Termination resistors are used at each end of the cable. The worst-case transmission time of an 8-byte frame with an 11-bit identifier is 134 bit times (that's 134 microseconds at the maximum baud rate of 1Mbits/sec).




    The CAN Bus interface uses an asynchronous transmission scheme controlled by start and stop bits at the beginning and end of each character. This interface is used, employing serial binary interchange. Information is passed from transmitters to receivers in a data frame. The data frame is composed of an Arbitration field, Control field, Data field, CRC field, ACK field. The frame begins with a 'Start of frame' [SOF], and ends with an 'End of frame' [EOF] space. The data field may be from 0 to 8 bits. The frame check sequence is derived from a Cyclic Redundancy Code (CRC); the coefficients are generated modulo-2: X15 + X14 + X10 + X8 + X7 + X4 + X3 + 1. CAN implements five error detection mechanisms; 3 at the message level and 2 at the bit level [Also incorporates error flags]. At the message level: Cyclic Redundancy Checks (CRC), Frame Checks, Acknowledgment Error Checks. At the bit level: Bit Monitoring, Bit Stuffing. The CANbus pinout is shown in the table below.
    The Application for CAN bus in the automotive area include;
    A low speed CANbus may be employed to operate window and seat controls. A high speed CANbus may be employed for engine management or brake control. Many other applications are possible [Engine Sensors, Anti-Skid Systems].

  6. #6
    Regular Member RSV_Ecosse's Avatar
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    Thanks.

    That means absolutely nothing to me!!!.

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    [Ex]Admin Duncan's Avatar
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    Hope willco's reply answers your question wardy?!

    RSV - half-CanBus means that there are still some 'proper' electrical parts in the car. One example is the headlight switch. On a half-CanBus car there is a +12V feed going in there and the headlight switch itself is a proper switch i.e has the 12V passing through it. The fog light switches are CanBus i.e. push them and they send a data signal elsewhere in the car to then activate the correct relay etc. to switch them on. So the module is half-CanBus.

    On a full CanBus car the headlight switch doesn't have a +12V going into it, the headlight switch will just send data (like the fog switches do) to the relevant place. Therefore the headlight switch is a full CanBus module.

    I hope I got all that correct!

    There are other items affected on a full CanBus car - the head unit to name one.

    CanBus is simply a data bus used to send information around the car to various modules to get them to do certain things relevant to the operation of the car.

    It also allows clever little tricks like this. If a rear tail-light goes, the car senses it. It then feeds a signal to the relevant module to instead tell it to use a different bulb (think it's the brake light) to act as the tail-light by feeding it a lower voltage. It will still light up brighter when the brakes are applied. I think I've got that the right way around - as opposed to the tail-light working as a failed brake light! Maybe it will do both! lol but you get the idea.

    D

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    Sounds spot on to me D. Well put.

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    Ex Vec-C Admin & Founder Bainie's Avatar
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    On mine when you switch off the headlamps it takes about 1/2 a second to tell the relevent gizmo and actually turn them off, it`s very strange !! you are used with things going off/on when you hit a switch.,,

    On another note, if you have buttons on your steering wheel for the volume control you are 1/2 and a little wheel is full ...

  10. #10
    Regular Member RSV_Ecosse's Avatar
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    Mine is a November 2004 and has buttons on the wheel, so its half-canbus.

    What difference does that make ( if any ) to modifying things and fiddling with the electrical side ( say for HID's or any other elec accessory ) , if its half canbus as oppossed to canbus?.

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