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Modbus

An industrial communications protocol used for connecting industrial electronic devices. Available in Master and Slave packages.

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Features

Currently available for Micrium µC/OS-II and µC/OS-II. Support for µC/OS 5 coming soon.

About Modbus

With Modbus, you can use either ASCII frames or RTU frames, or both at at the same time if you have multiple serial interfaces. Micrium's Modbus module supports any number of communications channels.

Modbus-S is a Modbus Slave (server) software component enabling an embedded system to communicate to a Modbus Master (client).

Modbus-M is a Modbus Master (client) component that enables communication to a Modbus Slave.

Micrium's Modbus module enables a developer to read or write integer, floating-point (assuming Daniels extensions) and discrete values from and to the target system.

modbus_schematic

Key Features

The features of Micrium's Modbus module include:

  • Allows for multiple RS-232C and/or RS-485 ports on the same target (limited only by the number of serial ports available)
  • The baud rate for each port is independently adjustable.
  • Select either Modbus ASCII or RTU on a per-channel basis.
  • Easily assign nearly any application variable to any Modbus holding register (up to 65536), input register (up to 65536), coil (up to 65536) or input status (up to 65536).
  • Complete, clean ANSI C source code included
  • Scalable from 6K to 15K bytes. Compile only the function codes necessary for the target.
  • Works with any CPU (8-, 16-, 32-, 64-bit or DSP)
  • Works with or without an RTOS kernel
  • Easily configurable

Specifications

Key Specifications

  • Unlimited number of ‘channels’ (limited only by the number of serial interfaces)
  • ASCII or RTU mode selectable on a per-channel basis
  • Floating-point support through “Daniel’s Extensions”
  • Modbus Slave or Master possible on the same product
  • Adjustable baud rate on a per channel-basis
  • Easily assign application variables to modbus registers, coils and discrete inputs.
  • Works with any processor (8-, 16-, 32-, 64-bit or DSP)
  • Works with or without an RTOS kernel
  • Easily configurable
  • ANSI C source code provided
  • Scalable from 6K to 15K bytes of code space.

Function Codes

Supported Modbus function codes:

Function Code Description
1 Coil Read
2 Discrete Input Read
3 Holding Register Read
4 Input Register Read
5 Write Single Coil
6 Write Single Holding Register
8 Diagnostic Loopback
15 Write Multiple Coils
16 Write Multiple Holding Registers
20 File Read
21 File Write

Licensing

Licensing Packages That Meet Your Needs

Check out our licensing page for more information.

Documentation

Micrium's user documentation for Micrium OS is available online on the Micrium documentation site.

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