Modbus General
Good Resources http://www.rtaautomation.com/modbusrtu/ http://www.rtaautomation.com/modbustcp/ Serial Modbus Serial MODBUS connections can be ASCII and RTU (binary coded). Modbus RTU: Messages are a...
View ArticleModbus TCP/IP
Resources Acromag Introduction To Modbus TCP/IP Has a good explanation of how a RTU serial packet is transferred over TCP/IP modbus.org Modbus Messaging On TCP/IP Implementation Guide Simply Modbus...
View ArticleModbus Comms General
Resources modbus.org Modbus Application Protocol Describes function codes modbus.org Modbus over Serial Line Specification and Implementation Guide Register Addressing The Modbus register number...
View ArticleFunction 03 Read Holding Registers
Modbus RTU Function 03 'Read Holding Registers' To read a word (16 bits) from a register you send the following: Byte 0 Modbus Device Address (1 to 247) Byte 1 Function Code / Message Type (0x03) Byte...
View ArticleFunction 06 Write Single Register
Modbus RTU Function 06 'Preset Single Register' To write a word (16 bits) to a register you send the following: Byte 0 Modbus Device Address (1 to 247) Byte 1 Function Code / Message Type (0x06) Byte...
View ArticleFunction 16 Write Multiple Registers
Modbus RTU Function 16 'Preset Multiple Registers' To write 3 words (48 bits) to 3 consecutive registers you send the following: Byte 0 Modbus Device Address (1 to 247) Byte 1 Function Code / Message...
View ArticleModbus Apps
Free sourceforge.net/projects/qmodmaster/ Nice interface but only works with single register values (no float, ASCII strings etc support) Paid simplymodbus.ca/RTUmaster.htm Poor operation in Windows...
View ArticleByte ordering
Modbus is a big-endian protocol. The more significant byte of a 16-bit value is sent before the less significant byte So, for bytes on the bus a UInt16 is sent like this: Bits15:8 | Bits7:0...
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