An open data communication protocol developed in 1979 Published by Modicon Open structure Flexible Widely known Supplied by many SCADA and HMI software Have OPC Servers 2 serial transmission modes: ASCII 10 bits RTU (Binary) 11 bits Communication interface RS-232/485 Ethernet (TCP/IP) Station Device: 0 ~ 255 Digital 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. | Supervisory Control & Data Acquisition Communication Technology Modbus Protocol What is Modbus ? An open data communication protocol developed in 1979 Published by Modicon Open structure Flexible Widely known Supplied by many SCADA and HMI software Have OPC Servers 2 serial transmission modes: ASCII 10 bits RTU (Binary) 11 bits Communication interface RS-232/485 Ethernet (TCP/IP) Application structure (general) Modbus Device (Slave) Modbus Device (Slave) Internet RS-232/485 HMI SCADA Modbus Client (Master) Query-Response Cycle Station Number Data Bytes (Flexible) Error Check Station Number Function Code Data Bytes (Flexible) Error Check Query Response Function Code Hardware classification Station Device: 0 ~ 255 Digital 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 . | Supervisory Control & Data Acquisition Communication Technology Modbus Protocol What is Modbus ? An open data communication protocol developed in 1979 Published by Modicon Open structure Flexible Widely known Supplied by many SCADA and HMI software Have OPC Servers 2 serial transmission modes: ASCII 10 bits RTU (Binary) 11 bits Communication interface RS-232/485 Ethernet (TCP/IP) Application structure (general) Modbus Device (Slave) Modbus Device (Slave) Internet RS-232/485 HMI SCADA Modbus Client (Master) Query-Response Cycle Station Number Data Bytes (Flexible) Error Check Station Number Function Code Data Bytes (Flexible) Error Check Query Response Function Code Hardware classification Station Device: 0 ~ 255 Digital 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 Error Check Field Longitudinal Redundancy Check (LRC) RTU Mode Data system 8-bit Binary, 00~FF Bits per data unit Error Check Field Cyclical Redundancy Check (CRC) 1 Start Bit 7 Data Bits 1 Parity Bit (Even/Odd) 1 Stop Bit 1 Start Bit 7 Data Bits 2 Stop Bit 1 Start Bit 1 Start Bit 8 Data Bits 8 Data Bits 1 Parity Bit (Even/Odd) 1 Stop Bit 2 Stop Bit Modbus Message Packet ASCII Mode RTU Mode Modbus Plus network Byte 0, 1: transaction ID – usually 0 Byte 2, 3: protocol ID = 0 Byte 4, 5: number of bytes following Station Number Function Code Data Error Check End 2 Chars 2 Chars n Chars 2 Chars 2 Chars Start 1 Char : LRC CR,LF Station Number Function Code Data Error Check End 8 Bits 8 Bits n
