英语翻译Message frame for standard format (CAN Specification 2.0

英语翻译
Message frame for standard format (CAN Specification 2.0A) Message frame formats The CAN protocol supports two message frame formats,the only essential difference being in the length of the identifier (ID).In the standard format the length of the ID is 11 bits and in the extended format the length is 29 bits.The message frame for transmitting messages on the bus comprises seven main fields.A message in the standard format begins with the start bit "start of frame",this is followed by the "arbitration field",which contains the identifier and the "RTR" (remote transmission request) bit,which indicates whether it is a data frame or a request frame without any data bytes (remote frame).The "control field" contains the IDE (identifier extension) bit,which indicates either standard format or extended format,a bit reserved for future extensions and - in the last 4 bits - a count of the data bytes in the data field.The "data field" ranges from 0 to 8 bytes in length and is followed by the "CRC field",which is used as a frame security check for detecting bit errors.The "ACK field" comprises the ACK slot (1 bit) and the ACK delimiter (1 recessive bit).The bit in the ACK slot is sent as a recessive bit and is overwritten as a dominant bit by those receivers which have at this time received the data correctly (positive acknowledgement).Correct messages are acknowledged by the receivers regardless of the result of the acceptance test.The end of the message is indicated by "end of frame"."Intermission" is the minimum number of bit periods separating consecutive messages.If there is no following bus access by any station,the bus remains idle ("bus idle").Detecting and signalling errors Unlike other bus systems,the CAN protocol does not use acknowledgement messages but instead signals any errors that occur.For error detection the CAN protocol implements three mechanisms at the message level:Cyclic Redundancy Check (CRC) The CRC safeguards the information in the frame by adding redundant check bits at the transmission end.At the receiver end these bits are re-computed and tested against the received bits.If they do not agree there has been a CRC error.Frame check This mechanism verifies the structure of the transmitted frame by checking the bit fields against the fixed format and the frame size.Errors detected by frame checks are designated "format errors".ACK errors As mentioned above,frames received are acknowledged by all recipients through positive acknowledgement.If no acknowledgement is received by the transmitter of the message (ACK error) this may mean that there is a transmission error which has been detected only by the recipients,that the ACK field has been corrupted or that there are no receivers

标准格式(能规格2.0A)消息框架的消息框架格式化罐头协议支持二个消息框架格式,唯一的根本区别在标识符(ID)的长度.以标准格式ID的长度是11位,并且在延长的形式长度是29位.传送的消息的消息框架在公共汽车包括七个主要领域.一则消息以标准格式从起始点“开始开始框架”,这由“仲裁领域”跟随,包含标识符和“RTR” (遥远的传输请求)没有任何数据字节(遥远的框架),位,表明它是否是数据帧或请求框架.“控制域”包含IDE (标识符引伸)位,表明标准格式或延长的形式、为未来引伸预留的位和-在前4位-数据字节一计数在数据域的.“数据域”从0范围到长度8个字节和由“CRC领域”跟随,使用作为框架安全检查为查出比特差错.“ACK领域”包括ACK槽孔(1位)和ACK符号(1隐性位).在ACK槽孔的位被送作为隐性位和由有在恰当地接受时间数据的这的那些接收器重写,当统治位(肯定回答).不管验收试验的结果正确消息由接收器承认.消息的末端由“框架的末端”表示.“间歇”是位期间的最小数字分离连贯消息的.如果没有跟随的公共汽车通入由任何驻地,公共汽车保持无所事事(“公共汽车懒惰”).查出和发信号不同于其他总线系统的错误,罐头协议不使用承认消息,反而发信号生成的所有错误.为错失侦查罐头协议实施三个机制在消息层：周期性多余信息检验(CRC) CRC通过增加冗余检验位保障在框架的信息在传输末端.在接收器末端这些位重新计算并且被测试反对被认为标准的比特.如果他们不同意有CRC错误.框架检查这个机制通过检查位领域核实被传送的框架的结构反对固定形式和帧大小.框架检查查出的错误被选定“格式错误”.ACK错误如上所述,被接受的框架由所有接收者承认通过肯定回答.如果承认没有由消息接受(ACK错误)的发射机这也许意味有接收者仅查出了的传输错误,ACK领域腐败了或没有接收器