Hongke share | bring you a comprehensive understanding of "can bus error" (II) -- can error types

In this series of articles , We will give you a detailed introduction to CAN Knowledge about bus errors , Include CAN The basic concept of bus error 、CAN Type of bus error 、CAN Error frame and CAN Node error status , And generate and record through the actual application test CAN error .

CAN Wrong type

CAN The bus protocol specifies 5 Kind of CAN Wrong type ：

• Bit error [ transmitter ]
• Bit fill error [ Receiver ]
• Format error [ The receiver ]
• ACK Wrong answer （ The reply ）[ transmitter ]
• CRC Check error （ Cyclic redundancy check ）[ Receiver ]

In the last article ” Hongke sharing | Bring you a comprehensive understanding “CAN Bus error ”（ One ）——CAN Bus errors and error frames “ in , We have learned something about bit errors and bit filling errors , Both are evaluated at the incumbent level . The other three CAN Error types are evaluated at the message level .

Next, we will introduce each error type in detail .

1） Bit error

CAN Each on the bus CAN The node will monitor the signal level at any given time —— This means sending CAN Nodes will also “ Read back ” It sends every bit . If the data bit level read by the transmitter is different from the content it sends , Then the transmitter will detect it as a bit error . however , If in the course of arbitration （ Send CAN ID when ） Bit mismatch occurs , It will not be interpreted as a bit error . Similarly , Reply slot （ACK Field ） Mismatches in do not cause bit errors , because ACK The field specifically requires that the recessive bits from the transmitter be overwritten by the dominant bits from the receiver .

2） Bit fill error

As mentioned earlier , Bit padding is CAN Part of the standard . It stipulates that every at the same logical level 5 After consecutive bits , The first 6 Bits must be complements . This is necessary to ensure continuous synchronization of the network by providing a rising edge . Besides , It ensures that the bit stream is not misunderstood as an error frame or the inter frame space marking the end of the message （7 Bit recessive sequence ）. all CAN Nodes will automatically delete redundant bits .
If in CAN In message （ stay SOF and CRC Between fields ） A with the same logic level is observed on the bus of 6 Bit sequence , Then the receiver detects it as a bit filling error , That is, filling errors .

3） Format error

This message level check utilizes CAN Some fields in the message / The fact that bits must always be at some logical level . say concretely ,1 position SOF Must be explicit , And the whole 8 position EOF Fields must be implicit . Besides ,ACK and CRC Delimiters must be implicit . If the receiver finds that any of these bits has an invalid logic level , Then the receiver detects it as a format error .

4） ACK Wrong answer （ The reply ）

When the transmitter sends CAN When the message , It will contain ACK Field （ The reply ）, The transmitter will send a hidden bit . All listening CAN Nodes should send dominant bits in this field to verify the receipt of messages （ Whether or not the node is interested in the message ）. If the transmitter does not read ACK Dominant bit in time slot , Then the transmitter will detect it as ACK error .

5） CRC Check error （ Cyclic redundancy check ）

Every CAN Each message contains a 15 Bit cyclic redundancy checksum field . ad locum , The transmitter has calculated CRC Value and add it to the message . Each receiving node will also calculate CRC. If the receiver CRC Calculate with the transmitter CRC Mismatch , The receiver will detect it as CRC error .

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