MODBUS

Being the industry standard since 1979, millions of devices use MODBUS for reliable industrial communication. MODBUS is an application level protocol positioned at level 7 of the Open Systems Interconnection (OSI) model. It supports client/server communication between devices connected on RS485/RS422 or TCP/IP networks.
 
MODBUS is a request/reply protocol where different functions provide a set of standardized services and, if required, can be extended by application-specific services. The standardized services include a pre-defined data model suitable for the exchange of analog and digital information. 
 
The four primary elements of the data model are:
  • 1-bit read only discrete inputs (e.g. the state of a digital input)
  • 1-bit read/write coils (e.g. an digital output)
  • 16-bit read only input registers (e.g. the value of an analog input)
  • 16-bit read/write holding registers (e.g. the analog output value of an actuator)
In addition, the standard includes a large set of supporting diagnostic services and additional data types (File records, FIFOs, etc.).

Features

  • No product royalties

  • Full source code provided

  • Support two different serial APIs optimally supporting RTOS/no RTOS operating systems.

  • Conforming to MODBUS application protocol V1.1

  • Supports MODBUS RTU/ASCII

  • Supports MODBUS TCP

  • Supports MODBUS UDP


  • Low resource overhead with only a few kilobytes of flash and ~300 bytes of RAM per instance


  • Supports multiple instances on a single platform


  • MASTER and SLAVE stack share the same porting layer

     
  • MASTER and SLAVE stack can run in parallel

     
  • An unlimited number of MODBUS slave devices can be polled
  • Supports a blocking and non-blocking API
  • Optimized ports for Windows/Linux resulting in low RTU round trip times allowing the polling of a large number of devices
  • Can be extended by custom function codes
  • Supports MODBUS TCP/RTU gateway mode (requires master license)
  • Optimized ports for Windows/Linux which uses RTU frame inspection and runtime CRC checking resulting in low RTU round trip times
  • Can be extended by custom function codes
 
  • Embedded platforms with no operating systems (AVR, MSP430, PIC32, ARM Cortex (Atmel, Freescale, ST, NXP and others), 8051 and others
  • Embedded platforms with RTOS (FreeRTOS, ucOS-II, Keil RTX and others
  • Operating systems (Windows, Linux and others)

MODBUS Master online purchase & free evaluation version:

MODBUS Slave online purchase & free evaluation version:

MODBUS documentation: