毕业论文外文翻译之modbus通讯协议

毕业论文外文翻译之modbus通讯协议内容摘要：

a group holding registers, the code will produce the following functions: 00000011 (hexadecimal 03H) Normal response es from the device to respond only to the same function code. Objection response, it returns: 10000011 (hexadecimal 83H) In addition to the error function code has been modified due to objections, the response message into the data field from the device a unique code, which can tell the master what error occurred. After the master device applications get dissent response typical process is re filing, or diagnostic messages sent from the device and reported to the operator. 5) The data field Data Domain is a collection of two hexadecimal digits, in the range 00 ... FF. Network transmission mode which can be posed of a pair of ASCII characters or characters of a RTU. Sent from the master device contains additional information from the data field device message: From the equipment must be used for performing the functions defined by the code should do. This includes noncontiguous register addresses to the actual number of bytes of data the number of items in the domain to deal with. For example, if the primary device needs to read a group of holding registers (function code 03) from the device, the data field specifies the starting register and quantity of registers to be read. If you write a group from the master device registers (function code 10 hex), the data field is specified in the starting register and write the number of registers to write, the number of data bytes of data fields, to write to register data. If no error occurs, the device returns from the data field contains the data from the request. If an error occurs, this field contains an exception code。 the master application can be used to determine the next course of action to take. A data field in the message may not exist (zero length). For example, the master asked to respond to munications from the device event log (function code OB hex), and any additional information from the device without. 6) Error detection field There are two standard Modbus work error detection methods. Depending on the contents of the error detection field detection method may be selected. ASCII Elected to use ASCII mode for the character frame error detection field contains two ASCII characters. This is done using LRC (Longitudinal Redundancy Detection) method is calculated for the content of the message, not including start and colon carriage return character. LRC character appended to the front carriage return. RTU Elected as a character frame with RTU mode, error detection field contains a 16Bits value (two 8 bit characters Realization). An error detection field of the message content by cyclic redundancy check method derived. Additional CRC field at the end of the message, the low byte first and then when you add the high byte. Therefore, the high byte CRC is the last byte to send a message. 7) Continuous transmission of characters When news of the standard Modbus series of work transmission, each character is sent in the following manner (left to right): the least significant bit ⋯ most significant bit ASCII characters when using the frame bit sequence is: 5. Detection Errors may occur in munication systems in two ways: transmission errors。 programming or operator error. Modbus systems have dedicated these two error handling. Communication error generally refers to digital packets in a change in circumstances packets to add or reduce the number of bits is rare. The most mon error is the noise caused by munication: munication channel unwanted electrical signals, electrical interference from the machine, damage to the channel, impulse noise (spikes) and so will generate such signals. Standard Modbus serial work use two error detection methods. Parity is available to each character frame detection (LRC or CRC) applies to the entire message. They were produced before the message is sent by the master device。 the device detects each character and the entire message frame from the receiving process. When parity or redundancy checks error detection munication, message processing will stop over. No further munication from the machine, this message is not generated response. Once a munication error occurs, the message will be regarded as unreliable. The program enables Modbus Modbus host system cannot receive a response to make the case Communication error must have occurred , the judge after a certain period of time . The length of this period of time depending on the baud rate, packet type from the scan time machine may be. Once the time is set to host programmed to automatically resending messages. Two Modbus RTU transmission mode ASC Ⅱ and RTU, their character formats are optional parity bit. The first nine data fields RTU mode is a parity bit ( 8 data bits, 1 parity bit )。 ASCI data fields to work for the first eight parity bits ( 7 data bits, a parity bits ) . If you do not use parity, no parity bit is sent. Modbus parity system is optional。 users configure the interface device, to deal with odd or even parity for proper selection. However, the configuration of all the devices in the system must use the same options. Modbus error checking system is to ensure the quality of data transmission. Not detected for detection of a parity error, the system uses the CRC: cyclic redundancy checks (CRC)。