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As CAN is a message oriented network, the CAN-Identifiers are used to identify the message and it’s priority, not the network node. However, higher layer protocols such as CANopen or SAE J1939 implement a node-addressing respectively a combination of message prioritization and node-addressing to separate the different message types (network management, process and service data).
In CAN networks all messages are sent as an broadcast, and filters are only implemented on receiver-side. This means, every device has the chance to see all messages. It depends on the application of the device which data is used and which data is ignored. Devices use filters to only receive messages which they need. This keeps CPU load low.
The IXXAT VCI driver supports all IXXAT CAN interfaces. Usually the board selection is set to automatic detection. So, no matter whether it is an internal PCI, PCIe, PCIe Mini or an external CANblue II, CAN@net/VCI or USB-to-CAN V2 – simply change the interface and start your application. There is no need to change your application.
There are two possibilities. Topology components such as the CAN repeater CAN-CR220 provide up to 4 kV of galvanic isolation which is sufficient for many customers with similar applications.
Applications who require an even higher separation can use two fiber-optic repeaters such as the CAN-CR210/FO. The optical transmission of CAN data provides a nearly unlimited galvanic isolation.
A galvanic isolation is an additional component in the communication path between CAN controller and CAN bus. Even fast components have delay times in the 50 ns range. This roughly corresponds to the signal propagation time of a 10 meter cable and must be considered by calculating the maximum cable length.
On the other hand, the galvanic isolation protects the CAN controller and thus the device from damages caused by overvoltage. This can be an electromagnetic interference, but also a potential difference in the network. Such potential differences may e.g. occur by using different power supplies for each device.
However, usually the benefits of a galvanic decoupling outweigh the disadvantages.
Receives a CAN controller a message on the CAN bus, it automatically sends an acknowledgment. Regardless whether the message was intended for this device or not. Due to this, the transmit node knows that the transmission was successful. However, this does not guarantee the error free reception of the message by the desired target node.
If a CAN PC interface is connected to the network, it will normally send an acknowledgment for each message received. For analyzing a network and to find errors, the PC Interface should not interfere in the communication. Since this can change the network behavior and worst case cover up the error. If "TX passive mode" is activated, the interface will only receive messages, without acknowledgement.
High-speed CAN is the "classic" CAN bus (according to ISO11898-2), used in many (industrial) applications. The bit rates, defined by the "CAN in Automation" user organization are ranging from 10 kbit/s up to 1 Mbit/s. CAN signals are transmitted differentially. Using high-speed CAN, the differential voltage for dominant bits is 2 V, for recessive bits 0 V.
A: The dominant level of the CAN-high wire is 3.5 V. B: The recessive level of CAN-high and CAN-low wires is 2.5 V. C: The dominant level of the CAN-low wire is 1.5 V.
Low-Speed CAN, or Fault-Tolerant CAN, is designed for improved durability. The recessive level of the differential signal is at -5 V, the dominant level is 2.2 V. If one of the two data lines is damaged, there is an automatic switchover to single-wire mode. This allows the system to be operated. The bit rates ranging from 40-125 kbit/s.
The maximum length of a stub line depends on the used bitrate. Lower bit rates allow to work with longer stub lines.
The maximum CAN bus length is the line lenght between the two devices with the largest distance between each other. At this, the stubs must be also added. The biggest problem of stubs are reflections which can distort or destroy CAN messages.
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