Communication between bus interface and computer (v) can bus

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1. Can Network Diagram

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1. What are the features of can?

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The can protocol has the following characteristics.

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(1) Multi-master control?

When the bus is idle, all cells can start sending messages (multi-master control). The first unit to access the bus can get the right to send (Csma/ca way).

When multiple cells start sending at the same time, the unit that sends the high-priority ID message is given the right to send.

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? (2) What is the message sent?

In the can protocol, all messages are sent in a fixed format. when the bus is idle, all units connected to the bus can start sending new messages. When more than two units start sending messages at the same time, according to the identifier (Identifier??). ID) determines the priority level. The ID does not represent the destination address of the send, but rather the priority of the message that accesses the bus. when more than two units start sending messages at the same time, each bit of each message ID is compared to a quorum-by-arbitration basis. The unit that wins the arbitration (which is judged to be the highest priority) can continue to send messages, and the unit that loses the quorum immediately stops sending and receives the work.

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? (3) What is the softness of the system?

The unit connected to the bus does not have information similar to "address". Therefore, when adding a unit to the bus, the hardware and software of the other units connected to the bus and the application layer need not be changed.

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(4) Communication speed?

Depending on the size of the entire network, you can set the appropriate communication speed.

in the same network, all units must be set to a unified communication speed. even if the communication speed of one unit is different from the others, the unit also outputs the wrong signal, which hinders the communication of the whole network. Different networks can have different communication speeds.

? (5) Remote Data request?

You can request other cells to send data by sending a "remote control frame"?

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(6) Error detection function • Error notification function • Error recovery function? All units can detect errors (Error detection function).

The unit that detects the error immediately notifies all other units (Error notification function) at the same time.

The unit that is sending the message will force the end of the current send once it detects an error. The unit that forces the end of the send will repeatedly resend the message until it has been successfully sent (Error recovery feature).

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? (7) fault closed?

Can determine whether the type of error is a temporary data error on the bus (such as an external noise, etc.) or a persistent data error (such as a unit internal failure, drive failure, disconnection, etc.). This feature allows the unit that caused this failure to be isolated from the bus when a continuous data error occurs on the bus.

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? (8) connection?

Can bus is a bus that can connect multiple units at the same time. The total number of cells that can be connected is theoretically unlimited. But the number of units that can actually be connected is limited by the time delay on the bus and the electrical load. Reduce communication speed, increase the number of connected cells, and increase the communication speed, the number of connected units can be reduced.

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Reference:

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1. Can bus protocol explanation

Communication between bus interface and computer (v) can bus