The low-order bit of the register (41 hex) The value of the upper register bit (AE hex) The number of bytes further (6 bytes follow) In response to the Modbus RTU Slave device we get: The number of required registers (reading 3 registers from 40108 to 40110) The address of the first register (40108-40001 = 107 = 6B hex) THE ADDRESS OF THE SLAVEID DEVICE (17 = 11 HEX) The following is an example of a Modbus RTU request for obtaining the AI value of the holding registers from registers # 40108 to 40110 with the address of the device 17. The difference between these two quantities is “offset”.Įach table has its own offset, respectively: 1, 10001, 3001. The Modbus message uses the register address.įor example, the first register of AO Holding Register has the number 40001, but its address is 0000. Two tables are read-only and two are read-write. SlaveID is the address of the device, it can take a value from 0 to 247, addresses from 248 to 255 are reserved.ĭata in the module is stored in 4 tables. If you discard the SlaveID address and the CRC checksum, you get the PDU, Protocol Data Unit.
Labview modbus code code#
The Modbus RTU message consists of the address of the SlaveID device, the function code, the special data, depending on the function code and the CRC of the checksum. It uses RS-485, RS-422, RS-232 interfaces, as well as Ethernet TCP / IP networks (Modbus TCP protocol) for data transfer. Modbus -communication protocol is based on the master-slave architecture. Equipment with Modbus RTU support Modbus RTU protocol description.Programs for working with Modbus RTU protocol.What are the errors of the Modbus request?.How can I send a Modbus RTU command to record multiple analog outputs? Command 0x10.How can I send a Modbus RTU command to write multiple discrete pins? Command 0x0F.How can I send a Modbus RTU command to record analog output? Command 0x06.How can I send a Modbus RTU command to write discrete output? Command 0x05.How can I send the Modbus RTU command to read the analog input? Command 0x04.How can I send a Modbus RTU command to read analog output? Command 0x03.How can I send a Modbus RTU command to read a digital input? Command 0x02.How can I send a Modbus RTU command to read discrete output? Command 0x01.Detailed description of the Modbus TCP protocol with command examples
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