can總線協(xié)議外文翻譯(編輯修改稿)
2024-12-12 01:53 本頁面
【文章內(nèi)容簡介】 type of frame is a Data Frame. This is used when a node transmits information to any or all other nodes in the system. Second is a Remote Frame, which is basically a Data Frame with the RTR bit set to signify it is a Remote Transmit Request. The other two frame types are for handling errors. One is called an Error Frame and one is called an Overload Frame. Error Frames are generated by nodes that detect any one of the many protocol errors defined by CAN. Overload errors are generated by nodes that require more time to process messages already received. Data Frames consist of fields that provide additional information about the message as defined by the CAN specification. Embedded in the Data Frames are Arbitration Fields, Control Fields, Data Fields, CRC Fields, a 2bit Acknowledge Field and an End of Frame. The Arbitration Field is used to prioritize messages on the bus. Since the CAN protocol defines a logical 0 as the dominant state, the lower the number in the arbitration field, the higher priority the message has on the bus. The arbitration field consists of 12bits (11 identifier bits and one RTR bit) or 32bits (29 identifier bits, 1bit to define the message as an extended data frame, an SRR bit which isunused, and an RTR bit), depending on whether Standard Frames or Extended Frames are being utilized. The current version of the CAN specification, version ,defines 29bit identifiers and calls them Extended Frames. Previous versions of the CAN specification defined 11bitidentifiers which are called Standard Frames. As described in the preceding section, the Remote Transmit Request (RTR) is used by a node when it requires information to be sent to it from another node. To acplish an RTR, a Remote Frame is sent with the identifier of the required Data Frame. The RTR bit in the Arbitration Field is utilized to differentiate between a Remote Frame and a Data Frame. If the RTR bit is recessive, then the message is a Remote Frame. If the RTR bit is dominant, the message is a Data Frame. The Control Field consists of six bits. The MSB is the IDE bit (signifies Extended Frame) 華北科技學(xué)院畢業(yè)設(shè)計 外文文獻及譯稿 第 5 頁 共 10 頁 which should be dominant for Standard Data Frames. This bit determines if the message is a Standard or Extended Frame. In Extended Frames, this bit is RB1 and it is next bit is RB0 and it is also reserved. The four LSBs are the Data Length Code (DLC) bits. The Data Length Code bits determine how many data bytes are included in the message. It should be noted that a Remote Frame has no data field, regardless of the value of the DLC bits. The Data Field consists of the number of data bytes described in the Data Length Code of the Control Field. The CRC Field consists of a 15bit CRC field and a CRC delimiter, and is used by receiving nodes to determine if transmission errors have occurred. The Acknowledge Field is utilized to indicate if the message was received correctly. Any node that has correctly received the message, regardless of whether the node processes or discards the data, puts a dominant bit on the bus in the ACK Slot bit time The last two message types are Error Frames and Overload Frames. When a node detects one of the many types of errors defined by the CAN protocol, an Error Frame occurs. Overload Frames tell the work that the node sending the Overload Frame is not ready to receive additional messages at this time, or that intermission has been violated. These errors will be discussed in more detail in the next section. Fast,
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