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Modbus/en: различия между версиями
Новая страница: «The Modbus data package looks as shown in the figure. A PDU (Protocol Data Unit) is a common part of a MODBUS package that includes the function code and data of…»
(Новая страница: «The Modbus data package looks as shown in the figure. A PDU (Protocol Data Unit) is a common part of a MODBUS package that includes the function code and data of…») |
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[[File:Modbus_Datagram.png|900px|thumb|left|Modbus datagram in general]] | [[File:Modbus_Datagram.png|900px|thumb|left|Modbus datagram in general]] | ||
The Modbus data package looks as shown in the figure. A PDU (Protocol Data Unit) is a common part of a MODBUS package that includes the function code and data of the package. '''ADU''' (Application Data Unit) is a complete Modbus package. Includes a physical layer-specific part of the package and PDU. For serial lines, the device address is passed in the ADU header, and the CRC16 checksum is passed at the end. The maximum ADU size in serial communication lines is 253 bytes (1 byte of the address and two bytes of the checksum are subtracted from the maximum 256 bytes allowed by the specification). For reference — in Modbus TCP, the maximum packet length is 260 bytes. | |||