FreeMODBUS - A Modbus ASCII/RTU and TCPimplementation
latest release v1.5 - 6 June2010
- Home- Examples- HW/SW requirements
- Ports ASCII/RTU- FreeRTOS/STR71X- AVRATMega8/16/32/128/168/169- Freescale MCF5235- TI MSP430- LPC214X- Z8 Encore!/Z8F6422- Win32- Linux/Cygwin- FreeRTOS/AT91SAM7X- HCS08- Atmel SAM3S
- Ports TCP- Win32- lwIP/MCF5235- lwIP/STR71X
- Documentation- API documentation
- Downloads
- Credits- Contact- Links
AboutFreeMODBUS is a free implementation of the popular Modbusprotocol specially targeted for embedded systems. Modbus is apopular network protocol in the industrial manufacturing environment.A Modbus communication stack requires two layers. The ModbusApplication Protocol which defines the data model and functions and aNetwork layer. In its current version FreeMODBUS provides animplementation of the Modbus Application Protocol v1.1a andsupports RTU/ASCII transmission modes defined in the Modbus overserial line specification 1.0. Since version 0.7 FreeModbus alsosupports Modbus TCP defined in Modbus Messaging on TCP/IPImplementation Guide v1.0a. It is licensed under the BSD[1] whichpermits its usage in commercial environments. The following Modbusfunctions are currently supported:
Read Input Register (0x04)Read Holding Registers (0x03)Write Single Register (0x06)Write Multiple Registers (0x10)Read/Write Multiple Registers (0x17)Read Coils (0x01)Write Single Coil (0x05)Write Multiple Coils (0x0F)Read Discrete Inputs (0x02)Report Slave ID (0x11)
The implementation is based upon the most recent standards andshould be fully standard compliant. Receiving and transmitting ofModbus RTU/ASCII frames is implemented as a state machineswhich is driven by callbacks from the hardware abstraction layer. Thismakes porting to new platforms easy. If a frame is complete it ispassed to the Modbus Application Layer where its content isinspected. Hooks are available in the Application Layer to add newModbus functions.If Modbus TCP is used the porting layer must send an event to theprotocol stack if a new frame is ready for processing. The protocolstack then calls a function which returns the received Modbus TCPframe and processes it. If valid a response is created and the portinglayer is supplied with the Modbus response. It should then send theresponse back to the client.
[1]:This excludes the demo applications which might be licenseddifferently.
InformationCommercial support is available from Embedded Solutions.
FreeMODBUS library and web page maintained by Christian Walter [wolti at sil dot at]BerliOS Logo
FreeMODBUS is sponsored and provided by embedded solutions
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