Supervisory Control & Data Acquisition - Communication Technology Modbus Protocol

An open data communication protocol developed in 1979Published by ModiconOpen structureFlexibleWidely knownSupplied by many SCADA and HMI softwareHave OPC Servers2 serial transmission modes:ASCII 10 bitsRTU (Binary) 11 bitsCommunication interfaceRS-232/485Ethernet (TCP/IP)Station Device: 0 ~ 255Digital input 1xxxx: 4 digits for hexadecimal address (0000 ~ FFFF)1xxxxx: 5 digital for decimal address (0 ~ 65535)Digital output0xxxx: 4 digits for hexadecimal address (0000 ~ FFFF)0xxxxx: 5 digital for decimal address (0 ~ 65535)Analog input4xxxx: 4 digits for hexadecimal address (0000 ~ FFFF)4xxxxx: 5 digital for decimal address (0 ~ 65535)Analog output3xxxx: 4 digits for hexadecimal address (0000 ~ FFFF)3xxxxx: 5...
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Supervisory Control & Data Acquisition - Communication Technology Modbus ProtocolSupervisory Control & Data Acquisition Communication Technology Modbus Protocol What is Modbus ?An open data communication protocol developed in 1979Published by ModiconOpen structureFlexibleWidely knownSupplied by many SCADA and HMI softwareHave OPC Servers2 serial transmission modes:  ASCII  10 bits  RTU (Binary)  11 bitsCommunication interface  RS-232/485  Ethernet (TCP/IP)Application structure (general) Modbus Client (Master) SCADA HMI Internet RS-232/485 Internet Modbus Device (Slave) Modbus Device (Slave)Query-Response Cycle Query Station Number Function Code Station Number Data Bytes (Flexible) Function Code Data Bytes (Flexible) Error Check Error Check Response Hardware classificationStation Device: 0 ~ 255Digital input  1xxxx: 4 digits for hexadecimal address (0000 ~ FFFF)  1xxxxx: 5 digital for decimal address (0 ~ 65535)Digital output  0xxxx: 4 digits for hexadecimal address (0000 ~ FFFF)  0xxxxx: 5 digital for decimal address (0 ~ 65535)Analog input  4xxxx: 4 digits for hexadecimal address (0000 ~ FFFF)  4xxxxx: 5 digital for decimal address (0 ~ 65535)Analog output  3xxxx: 4 digits for hexadecimal address (0000 ~ FFFF)  3xxxxx: 5 digital for decimal address (0 ~ 65535) Two serial transmission modes ASCII Mode Data system  ASCII character, ‘0’~’9’,’A’~’F’ Bits per data unit 1 Start Bit 7 Data Bits 1 Parity Bit (Even/Odd) 1 Stop Bit1 Start Bit 7 Data Bits 2 Stop Bit Error Check Field  Longitudinal Redundancy Check (LRC) RTU Mode Data system  8-bit Binary, 00~FF Bits per data unit 1 Start Bit 8 Data Bits 1 Parity Bit (Even/Odd) 1 Stop Bit1 Start Bit 8 Data Bits 2 Stop Bit Error Check Field  Cyclical Redundancy Check (CRC) Modbus Message Packet ASCII Mode Start Station Number Function Code Data Error Check End1 Char 2 Chars 2 Chars n Chars 2 Chars 2 Chars : LRC CR,LF RTU Mode Start Station Number Function Code Data Error Check End3.5 Char 8 Bits 8 Bits n x 8 Bits 2 x 8 Bits 3.5 CharsSilence CRC Silence Modbus Plus network Prefixed Data Station Number Function Code Data 6 x 8 Bits Byte 0, 1: transaction ID – usually 0 Byte 2, 3: protocol ID = 0 Byte 4, 5: number of bytes following Read/Write ModesSingle Read/WriteMultiple Read/Write Basic application #1 Modbus/TCP Clients (Masters) Modbus/TCP command protocol Internet InternetDefaultFirmware Modbus/TCP Slave Device Basic application #2 Modbus/TCP Clients (Masters) Serial Device Clients (Masters) Modbus/TCP command protocol Command protocol depend on serial devices Internet Internet Modbus/TCP Slave DeviceDefaultFirmware Serial Remote Device Virtual Comm TechniqueModbus SDK Modbus Embedded ControllerModbus Client (Master) Modbus protocol User-defined protocolSCADA HMI Modbus Embedded Controller Check Modbus Request Update I/O RS-485 Run User Process .. . RS-232 PLC Advanced application Modbus/TCP Clients (Masters) General TCP/IP Client (Masters) Serial Device Clients (Masters) Modbus/TCP Slave ...