test_rmd.rb

require "rmodbus"

s = ModBus::TCPServer.new(9999, 1)
s.holding_registers = [1] * 10
s.start

ModBus::TCPClient.connect('127.0.0.1',9999) do |cl|
  cl.with_slave(1) do |slave|
    slave.raise_exception_on_mismatch = true
    slave.debug =true
    begin
      puts slave.holding_registers[0..2]
      slave.holding_registers[0..1] = [0,0]
    rescue ModBus::Errors::ResponseMismatch => e
      puts e.msg, e.request, e.response
    end
  end
end

s.stop