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RS485 physical layer based on the MODBus / JBus field bus communication protocol

0 ∞ a word or read the value of digital word response [h0d1 hug 0x06 bytes n bytes to write to write the word Island vend valve 2.6 error handling pots are errors in the communication process, from the machine with the error code to identify the place the wrong kind. There are five error code on to describe error conditions occur: (1) Invalid command; (2) invalid parameter address; (3) parameters beyond the scope of valid values (not tested the reasonableness of parameters); ( 4) From the machine is not ready; (5) the parameters are write protected. Error response case, data packets from the machine structure shown in Table 2. Table 2 At this point, the function code 0x80 to do with the logical \The following error occurred when the machine does not produce responses from: (1) checksum (CRC16) error; (2) host the instruction is incomplete or is not defined in the instructions; (3) the words or the number of bits is zero. 2.7MODBus difference MODBus agreement with JBus JBus protocol is compatible with their data packet structure is the same. The only difference is their physical address data storage,ugg boots billig, said the difference is \JBus the same address and absolute address, for example, it is 1, MODBus address is 0. 2.8 Checksum (CRC16) checksum (CRC16) is used to identify transmission errors. If you found an error in the process, the device does not produce the corresponding response. In the data transmission is sent when the first checksum, the lowest level. NS CRC algorithm is shown in Figure 3. Figure 3 Figure 3CRC NS algorithm supported data types There are four data types, namely: (1) character data (Char): In principle, that only ASCII characters can be sent. They are stored in memory in accordance with the order being sent. (2) integer (Int): integer with 2 bytes (ie a word) to represent. In transmission,ugg prezzo, the high the first to be sent. (3) floating-point data (Float): Float 4 bytes (ie, two words) to represent. Measurement Technology of China in January 2OO6 when the host runs on IEEE. 754 format, before sending a floating-point, high words and low words will be exchanged position to make their order and MODBus mode of will. (4) byte-type data (Byte): This type of data used to represent the state identifiers, they can only use 8bit data to be transmitted, and transmission, to add a zero in front of bytes ( 0x00). 4, the host communication program communication protocol as simple JUMO, VB programming language can be easily achieved the host function. Using VB's MSCOMM control status can be a good bus to complete the send and receive binary data; TIMER control can be achieved by identifying the data frame, and then to the master control program analysis. Introduced here only a simple monitoring program to achieve the monitoring of data streams on the bus, you can also use it to mimic the host to send commands from the machine to get the desired data or simple control. NS procedure shown in Figure 4.5 Conclusion JUMO communication protocol is characterized by the parameters of the equipment to read and modify through direct memory address of the corresponding operation to complete, and it stopped by transfer to mark the end of the frame, so the protocol is simple, easy to implement. In addition,ugg milano, it uses a short frame, transmission time is short, the probability of interference is low, and has good error detection results. Error detection by CRC, measures to ensure that the data error rate is very low. JUMO proved using communication protocols, can control system is located in the center from the station master and efficient, stable and reliable connection together, and to ensure communication between them and the data exchange without asking the host communication program in Figure 4 NS Figure caption so that all devices can operate stably. References [1] Zhang Bing,stivali ugg, Su Yanchen. RS485 bus,ugg stivali, microcomputer-based technology two-way communication with the intelligent instrument design [J]. China Measurement Technology, 2005,31 (1) :84-91. [2] Wang Jinbiao. Field bus and field bus control system [J]. Process Automation Instrumentation, 1997,24 (2) :3-7. [3] Xie Xiren. Computer Networks (second edition) [M]. Beijing: Electronic Industry Press, 1999. [4] JUMO temperature controller manual. [5] Meng Kaiyuan. Modbus communication protocol in the CRC checksum algorithm for fast c language [J]. Fujian computer, 2OO4 ,11:63-64. [6] section of German power. Fieldbus and Fieldbus Control Technology [J]. Information Technology, 2003,27 (3) :25-29.

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