RModBus

RModBus - free implementation of protocol ModBus.

Features

• Ruby 1.8, Ruby 1.9, JRuby (without serial ModBus RTU)
• TCP, RTU, RTU over TCP protocols
• Client(master) and server(slave)
• 16, 32 -bit and float registers

Support functions

• Read Coils (0x01)
• Read Discrete Inputs (0x02)
• Read Holding Registers (0x03)
• Read Input Registers (0x04)
• Write Single Coil (0x05)
• Write Single Register (0x06)
• Write Multiple Coils (0x0F)
• Write Multiple registers (0x10)
• Mask Write register (0x16)

Installation

Download and install RModBus with the following

$ gem install rmodbus

Example

require 'rmodbus'

ModBus::TCPClient.new('127.0.0.1', 8502) do |cl|
  cl.with_slave(1) do |slave|
    # Read a single holding register at address 16
    slave.holding_registers[16]

    # Write a single holding register at address 16
    slave.holding_registers[16] = 123

    # Read holding registers 16 through 20
    slave.holding_registers[16..20]

    # Write holding registers 16 through 20 with some values
    slave.holding_registers[16..20] = [1, 2, 3, 4, 5]
  end
end

Conversion to/from 32bit registers

Some modbus devices use two registers to store 32bit values. RModbus provides some helper functions to go back and forth between these two things when reading/writing. The built-in examples assume registers in a particular order but it's trivial to change.

# Reading values in multiple registers (you can read more than 2 and convert them all so long as they are in multiples of 2)
res = slave.holding_registers[0..1]
res.inspect => [20342, 17344]
res.to_32i => [1136676726]
res.to_32f => [384.620788574219]

# Writing 32b values to multiple registers
cl.holding_registers[0..1] = [1136676726].from_32i
cl.holding_registers[0..1] => [20342, 17344]
cl.holding_registers[2..3] = [384.620788574219].from_32f
cl.holding_registers[2..3] => [20342, 17344]

GitHub

You can checkout source code from GitHub repositry

$ git clone git://github.com/flipback/RModBus.git

Reference

Home page: http://rmodbus.heroku.com

RModBud on GitHub: http://github.com/flipback/RModBus

ModBus community: http://www.modbus-ida.org