Modbus TCP slave example

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Simple example of how to implement Modbus TCP slave via a resident script (sleep time = 0). It only supports binary objects as coils and 1-byte / 2-byte integer objects as registers. Number of coils and registers is not limited, object mapping can be set by filling coils, registers and regdt tables.

Code:

if not mb then
  require('genohm-scada.eibdgm')
  require('luamodbus')

  -- list of coil mapping, starting from 0
  coils = { '1/1/1', '1/1/2' }

  -- list of register mapping, starting from 0
  registers = { '2/2/2', '3/3/3' }

  -- list of register data types, element count must match registers table
  regdt = { dt.int8, dt.uint16 }

  -- knx group write callback
  function knxgroupwrite(event)
    local value

    -- try to find matching coil
    for id, addr in ipairs(coils) do
      if event.dst == addr then
        value = knxdatatype.decode(event.datahex, dt.bool)
        mb:setcoils(id - 1, value)
      end
    end

    -- try to find matching register
    for id, addr in ipairs(registers) do
      if event.dst == addr then
        value = knxdatatype.decode(event.datahex, regdt[ id ])
        mb:setregisters(id - 1, value)
      end
    end
  end

  -- coil write callback
  function mbwritecoils(coil, value)
    local addr = coils[ coil + 1 ]
    if addr then
      grp.write(addr, value, dt.bool)
    end
  end

  -- register write callback
  function mbwriteregisters(register, value)
    local addr = registers[ register + 1 ]
    if addr then
      grp.write(addr, value, regdt[ register + 1])
    end
  end

  -- knx group monitor, handles group writes
  knxclient = eibdgm:new({ timeout = 0.1 })
  knxclient:sethandler('groupwrite', knxgroupwrite)

  -- modbus slave, listen on all interfaces and default port 502
  mb = luamodbus.tcp()
  mb:open('0.0.0.0', 502)

  -- setting slave id is optional
  -- mb:setslave(1)

  mb:setreceivetimeout(0.1)
  mb:setmapping(#coils, 0, #registers, 0)

  -- init coils
  for id, addr in ipairs(coils) do
    value = grp.getvalue(addr)
    mb:setcoils(id - 1, value)
  end

  -- init registers
  for id, addr in ipairs(registers) do
    value = grp.getvalue(addr)
    mb:setregisters(id - 1, value)
  end

  -- set callbacks for coil and register write
  mb:setwritecoilcb(mbwritecoils)
  mb:setwriteregistercb(mbwriteregisters)
end

-- handle modbus and knx
mb:handleslave()
knxclient:loop(0.1)