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Universal Modbus TCP/RTU Slave - Printable Version

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RE: Universal Modbus TCP/RTU Slave - djaval - 27.03.2024

(26.02.2024, 09:08)Daniel Wrote: This is how it meant to work. You need to convert it back to float on master device.
mb.setfloat16precision(2) sets how float16 is converted to integer. By default it's 2 decimals (0.01 precision). Change 2 to 0 to convert to integer without any decimals.

Hi! Yes, it works. Not a big problem to convert back to float on master device, but just to clarify. Is it possible to make pure float register (either it can be little or big endian)?

RE: Universal Modbus TCP/RTU Slave - admin - 28.03.2024

float32 data type is handled as is without any conversion. The script can be modified to convert float16 to float32 instead of int16.

Edit: script has been updated with optional conversion of float16 to float32: https://kb.logicmachine.net/integration/modbus-rtu-tcp-slave/

RE: Universal Modbus TCP/RTU Slave - Krstfr2k - 12.06.2024

How do i set up the script to use slave id 1 on the first RS-485 port and slave id 2 on the second RS-485 port on an LM5 Lite?

RE: Universal Modbus TCP/RTU Slave - admin - 12.06.2024

Create two separate scripts, one for each port.

RE: Universal Modbus RTU - Ranjeet - 14.06.2024

I am Using Daikin Ac and Ac Guy Given me address and holding register ID. So query is that when I'm triggering from Logic Machine not getting response from AC. even i used json file.

RE: Universal Modbus TCP/RTU Slave - Daniel - 14.06.2024

This thread is for modbus slave and you are using master so if you have issues create dedicated topic for your case please.

RE: Universal Modbus TCP/RTU Slave - Ranjeet - 11.07.2024

Hi Sir,
When I am doing read test in Modbus in Logic Machine then it is showing me this number, what does it mean?
I have Attached Sceenshot

RE: Universal Modbus TCP/RTU Slave - Daniel - 11.07.2024

It is what the text says, result of the read request.

RE: Universal Modbus TCP/RTU Slave - Ranjeet - 12.07.2024

Thanks For Reply
sir I want to Know that how to understand this result and What it means

RE: Universal Modbus TCP/RTU Slave - admin - 12.07.2024

Check the register description in the device documentation.

RE: Universal Modbus TCP/RTU Slave - imprashant - 16.04.2025

We have 5 Zones in our project and each zone has an Automation DB having KNX Actuators and a KNX keypad.
So now we have to implement Auto/Manual logic in that way that if we press the button on KNX keypad the DB will go on the manual mode, it means now we are only able to control the DB devices (KNX Actuators) with keypad only and no command can be executed from the SCADA system until we remove the Manual mode by pressing the Auto mode key on the KNX keypad.
This Auto/Manual logic is to be implemented for all the 5 Zones.
Is it possible to make different resident script for different zone in MODBUS RTU so that we can disable the communication of particular zone by just disabling the resident script of that particular zone. We are using one LM5 as MODBUS RTU Slave for all 5 Zones.

RE: Universal Modbus TCP/RTU Slave - admin - 16.04.2025

Multiple resident scripts can't share the same RS-485 port. It should be enough just to block writing as needed.

Replace the whole handlers.writeregister function with this, modify writeallowed logic as needed.
Code:
local function writeallowed(slaveid)
  if slaveid == 1 then
    return grp.getvalue('1/1/1')
  elseif slaveid == 2 then
    return grp.getvalue('1/1/2')
  end
end

handlers.writeregister = function(slaveid, fncode, data)
  if #data ~= 4 then
    return
  end

  local addr = touint16(data, 1)
  local map = getmapping(slaveid, fncode)

  if not map or not map[ addr ] then
    return excodes.illegaldataaddress
  end

  local mapobj = map[ addr ]

  if mapobj.len ~= 1 then
    return excodes.illegaldataaddress
  end

  if writeallowed(slaveid) then
    writevalue(mapobj, data, 3)
  end

  return data
end

Replace the whole handlers.writeregisters function with this.
Code:
handlers.writeregisters = function(slaveid, fncode, data)
  if #data < 5 then
    return
  end

  local addr = touint16(data, 1)
  local count = touint16(data, 3)
  local bytes = touint8(data, 5)

  if #data ~= (bytes + 5) then
    return
  end

  if count == 0 or count > limits.writeregisters or bytes ~= count * 2 then
    return excodes.illegaldataaddress
  end

  local map = getmapping(slaveid, fncode)

  if not map then
    return excodes.illegaldataaddress
  end

  if writeallowed(slaveid) then
    for i = 0, (count - 1) do
      local mapobj = map[ addr + i ]

      if mapobj and not mapobj.readonly then
        local offset = 6 + i * 2
        writevalue(mapobj, data, offset)
      end
    end
  end

  return data:sub(1, 4)
end


RE: Universal Modbus TCP/RTU Slave - imprashant - 18.04.2025

Hi, I have done the changes in the mbslave (user library script). But still I didn't understand how will I disable one Zone to communicate with the SCADA  over modbus rtu. Do I need to make some changes in resident script as well. Please guide.

RE: Universal Modbus TCP/RTU Slave - imprashant - 21.04.2025

(18.04.2025, 15:16)imprashant Wrote: Hi, I have done the changes in the mbslave (user library script). But still I didn't understand how will I disable one Zone to communicate with the SCADA  over modbus rtu. Do I need to make some changes in resident script as well. Please guide.

Previously the script I was using was working but sometimes I have to send command 2-3 times from Modscan in order to execute command in LM5. The script I was using:

local mb = require('user.mbslave')
local mbrtu = require('luamodbus').rtu()

mbrtu:open('/dev/RS485-1', 9600, 'N', 8, 1, 'H')
mbrtu:connect()
mbrtu:setslave('*') -- Accept multiple RTU slave IDs

mb.setswap('w')
mb.setfloat16precision(2)

local ga1 = '0/0/11' --zone 1 enable/disable
local ga2 = '0/0/12' --zone 2 enable/disable
local current_mapping = nil

-- Predefine mappings for easy reuse
local mapping1 = {
    [1] = {
        coils = {
            [0] = '0/0/1',
        },
        registers = {
            [0] = '0/0/2',
        }
    }
}

local mapping2 = {
    [1] = {
        coils = {
            [1] = '0/0/3',
        },
        registers = {
            [1] = '0/0/4',
        }
    }
}

while true do
    local val1 = grp.getvalue(ga1)
    local val2 = grp.getvalue(ga2)

    if not val1 and current_mapping ~= "mapping1" then
        mb.setmapping(mapping1)
        current_mapping = "mapping1"
        log("Applied Mapping 1")
    elseif not val2 and current_mapping ~= "mapping2" then
        mb.setmapping(mapping2)
        current_mapping = "mapping2"
        log("Applied Mapping 2")
    end

    mb.rtuhandler(mbrtu)
    os.sleep(1) -- small delay to prevent CPU hogging
end

RE: Universal Modbus TCP/RTU Slave - admin - 22.04.2025

The previous solution is meant to be used with multiple slave IDs. Writing to slave ID 1 is allowed when 1/1/1 is true, writing to slave ID 2 is allowed when 1/1/2 is true. writeallowed should be modified as needed.

Alternative solution is to add logic AND gates to mapped group addresses.

Updated user library:
Code:
local _M = {}
local byteswap, wordswap
local f16mult = 1
local f16float = false
local mapping = {}
local exception = {}
local reply = {}

local fncodes = {
  [1] = 'readcoils',
  [2] = 'readdiscreteinputs',
  [3] = 'readregisters',
  [4] = 'readinputregisters',
  [5] = 'writecoil',
  [6] = 'writeregister',
  [15] = 'writecoils',
  [16] = 'writeregisters',
}

local mapfncodes = {
  [1] = 'coils',
  [2] = 'discreteinputs',
  [3] = 'registers',
  [4] = 'inputregisters',
  [5] = 'coils',
  [6] = 'registers',
  [15] = 'coils',
  [16] = 'registers',
}

local dtlens = {
  [ dt.bool ] = 1,
  [ dt.bit4 ] = 1,
  [ dt.int8 ] = 1,
  [ dt.uint8 ] = 1,
  [ dt.int16 ] = 1,
  [ dt.uint16 ] = 1,
  [ dt.float16 ] = 1,
  [ dt.int32 ] = 2,
  [ dt.uint32 ] = 2,
  [ dt.float32 ] = 2,
  [ dt.int64 ] = 4,
}

local maxpdu = 253
local maxaddr = 0x10000
local coilon = 0xFF00

local limits = {
  readbits = 2000,
  writebits = 1968,
  readregisters = 125,
  writeregisters = 123,
}

local excodes = {
  illegalfunction = 1,
  illegaldataaddress = 2,
  illegaldatavalue = 3,
  serverdevicefailure = 4,
  acknowledge = 5,
  serverdevicebusy = 6,
  negativeacknowledge = 7,
  memoryparityerror = 8,
  gatewaypathunavailable = 10,
  gatewaytargetdevicefailed = 11,
}

local handlers = {}

local function touint8(buf, off)
  return buf:byte(off)
end

local function touint16(buf, off, swap)
  local b1, b2 = buf:byte(off, off + 1)

  if swap then
    b1, b2 = b2, b1
  end

  return b1 * 0x100 + b2
end

local function getmapping(slaveid, fncode)
  local mapfncode = mapfncodes[ fncode ]
  local slave = mapping[ slaveid ]

  if not slave then
    slave = mapping['*']
  end

  if slave then
    return slave[ mapfncode ]
  end
end

local function readbits(slaveid, fncode, data)
  if #data ~= 4 then
    return
  end

  local addr = touint16(data, 1)
  local count = touint16(data, 3)

  if count == 0 or count > limits.readbits then
    return excodes.illegaldataaddress
  elseif (addr + count) > maxaddr then
    return excodes.illegaldataaddress
  end

  local map = getmapping(slaveid, fncode)

  if not map then
    return excodes.illegaldataaddress
  end

  local res = {}
  local bits, byte = 0, 0

  for i = 0, (count - 1) do
    local mapaddr = map[ addr + i ]

    if mapaddr then
      local bval = grp.getvalue(mapaddr)

      if toboolean(bval) then
        byte = byte + bit.lshift(1, bits)
      end
    end

    bits = bits + 1

    if bits == 8 then
      res[ #res + 1 ] = string.char(byte)
      bits, byte = 0, 0
    end
  end

  if bits ~= 0 then
    res[ #res + 1 ] = string.char(byte)
  end

  return string.char(#res) .. table.concat(res)
end

local zeroreg = string.char(0, 0)

local function readvalue(res, value, dpt)
  if dpt == dt.float16 then
    if f16float then
      dpt = dt.float32
    else
      value = value * f16mult
      dpt = dt.int16
    end
  end

  local enc = busdatatype.encode(value, dpt)
  if not enc.dataraw then
    return
  end

  local raw = enc.dataraw

  if #raw % 2 == 1 then
    local pad = value < 0 and 0xFF or 0
    raw = string.char(pad) .. raw
  end

  local words = #raw / 2
  local offset = #res

  for i = 1, words do
    local word = raw:sub(i * 2 - 1, i * 2)

    if byteswap then
      word = word:sub(2, 2) .. word:sub(1, 1)
    end

    if wordswap then
      res[ offset + i ] = word
    else
      res[ offset + 1 + words - i ] = word
    end
  end

  return true
end

local function readregisters(slaveid, fncode, data)
  if #data ~= 4 then
    return
  end

  local addr = touint16(data, 1)
  local count = touint16(data, 3)

  if count == 0 or count > limits.readregisters then
    return excodes.illegaldataaddress
  elseif (addr + count) > maxaddr then
    return excodes.illegaldataaddress
  end

  local map = getmapping(slaveid, fncode)

  if not map then
    return excodes.illegaldataaddress
  end

  local res = {}
  local max = count - 1

  while #res <= max do
    local mapobj = map[ addr + #res ]
    local success

    if mapobj then
      local value = grp.getvalue(mapobj.address)

      if type(value) == 'boolean' then
        value = value and 1 or 0
      end

      if type(value) ~= 'number' then
        alert('invalid value ' .. mapobj.address .. ' ' .. tostring(value))
        value = 0
      end

      success = readvalue(res, value, mapobj.dpt)
    end

    if not success then
      res[ #res + 1 ] = zeroreg
    end
  end

  if #res ~= count then
    return excodes.illegaldataaddress
  end

  return string.char(count * 2) .. table.concat(res)
end

local function writevalue(obj, data, offset)
  local words = obj.len
  local len = words * 2
  local raw = data:sub(offset, offset + len - 1)

  if #raw < len then
    return
  end

  local buf = {}

  for i = 1, words do
    local word = touint16(raw, i * 2 - 1, byteswap)
    local hex = string.format('%04X', word)

    if wordswap then
      buf[ #buf + 1 ] = hex
    else
      table.insert(buf, 1, hex)
    end
  end

  local hexval = table.concat(buf)
  local dpt = obj.dpt

  if dpt == dt.float16 then
    dpt = f16float and dt.float32 or dt.int16
  end

  local value = busdatatype.decode(hexval, dpt)

  if obj.dpt == dt.float16 and not f16float then
    value = value / f16mult
  end

  _M.write(obj.address, value)
end

handlers.readcoils = readbits
handlers.readdiscreteinputs = readbits

handlers.readregisters = readregisters
handlers.readinputregisters = readregisters

handlers.writecoil = function(slaveid, fncode, data)
  if #data ~= 4 then
    return
  end

  local addr = touint16(data, 1)
  local map = getmapping(slaveid, fncode)

  if not map or not map[ addr ] then
    return excodes.illegaldataaddress
  end

  local bval = touint16(data, 3) == coilon
  _M.write(map[ addr ], bval, dt.bool)

  return data
end

handlers.writeregister = function(slaveid, fncode, data)
  if #data ~= 4 then
    return
  end

  local addr = touint16(data, 1)
  local map = getmapping(slaveid, fncode)

  if not map or not map[ addr ] then
    return excodes.illegaldataaddress
  end

  local mapobj = map[ addr ]

  if mapobj.len ~= 1 then
    return excodes.illegaldataaddress
  end

  writevalue(mapobj, data, 3)

  return data
end

handlers.writecoils = function(slaveid, fncode, data)
  if #data < 5 then
    return
  end

  local addr = touint16(data, 1)
  local count = touint16(data, 3)
  local bytes = touint8(data, 5)

  if #data ~= (bytes + 5) then
    return
  end

  if count == 0 or count > limits.writebits or bytes ~= math.ceil(count / 8) then
    return excodes.illegaldataaddress
  end

  local map = getmapping(slaveid, fncode)

  if not map then
    return excodes.illegaldataaddress
  end

  local offset = 6
  local byte = data:byte(offset)
  local bits = 0

  for i = 0, (count - 1) do
    local bval = bit.band(bit.rshift(byte, bits), 1)
    local mapaddr = map[ addr + i ]

    if mapaddr then
      _M.write(mapaddr, bval, dt.bool)
    end

    bits = bits + 1
    if bits == 8 then
      bits = 0
      offset = offset + 1
      byte = data:byte(offset)
    end
  end

  return data:sub(1, 4)
end

handlers.writeregisters = function(slaveid, fncode, data)
  if #data < 5 then
    return
  end

  local addr = touint16(data, 1)
  local count = touint16(data, 3)
  local bytes = touint8(data, 5)

  if #data ~= (bytes + 5) then
    return
  end

  if count == 0 or count > limits.writeregisters or bytes ~= count * 2 then
    return excodes.illegaldataaddress
  end

  local map = getmapping(slaveid, fncode)

  if not map then
    return excodes.illegaldataaddress
  end

  for i = 0, (count - 1) do
    local mapobj = map[ addr + i ]

    if mapobj and not mapobj.readonly then
      local offset = 6 + i * 2
      writevalue(mapobj, data, offset)
    end
  end

  return data:sub(1, 4)
end

exception.tcp = function(sock, hdr, excode)
  local fncode = bit.bor(0x80, hdr:byte(8))
  local resp = hdr:sub(1, 4) ..
    string.char(0, 3) ..
    hdr:sub(7, 7) ..
    string.char(fncode, excode)

  return sock:send(resp)
end

exception.rtu = function(mbrtu, hdr, excode)
  local fncode = bit.bor(0x80, hdr:byte(2))
  local resp = hdr:sub(1, 1) ..
    string.char(fncode, excode)

  return mbrtu:send(resp)
end

reply.tcp = function(sock, hdr, data)
  local resp = hdr:sub(1, 4) ..
    string.char(0, #data + 2) ..
    hdr:sub(7, 8) .. data

  return sock:send(resp)
end

reply.rtu = function(mbrtu, hdr, data)
  local resp = hdr:sub(1, 2) .. data

  return mbrtu:send(resp)
end

local function handler(mode, ctx, hdr, data)
  local slaveid, fncode = hdr:byte(#hdr - 1, #hdr)
  local fnname = fncodes[ fncode ]

  if not fnname then
    return exception[ mode ](ctx, hdr, excodes.illegalfunction)
  end

  local res = handlers[ fnname ](slaveid, fncode, data)

  if type(res) == 'number' then
    return exception[ mode ](ctx, hdr, res)
  elseif type(res) == 'string' then
    return reply[ mode ](ctx, hdr, res)
  end
end

_M.tcphandler = function(sock)
  local hdr, err = sock:receive(8)

  if not hdr then
    return nil, err
  end

  local len = touint16(hdr, 5) - 2
  local data

  if len <= 0 or len > maxpdu then
    err = 'protocol error'
  else
    data, err = sock:receive(len)
  end

  if not data then
    return nil, err
  end

  return handler('tcp', sock, hdr, data)
end

_M.rtuhandler = function(mbrtu)
  local data, err = mbrtu:receive()

  if not data then
    return nil, err
  end

  local slaveid = data:byte(1)
  if not mapping[ slaveid ] then
    return
  end

  return handler('rtu', mbrtu, data:sub(1, 2), data:sub(3, #data - 2))
end

_M.setswap = function(swap)
  byteswap = swap:find('b') ~= nil
  wordswap = swap:find('w') ~= nil
end

_M.setfloat16precision = function(prec)
  prec = tonumber(prec) or 0
  f16mult = math.pow(10, prec)
end

_M.setfloat16mode = function(mode)
  f16float = mode == 'float'
  dtlens[ dt.float16 ] = f16float and 2 or 1
end

local function initobject(obj, dbobj)
  local dpt = obj.datatype or dbobj.datatype

  if type(dpt) == 'string' then
    dpt = dt[ dpt ] or 0
  end

  if type(dpt) == 'number' and dpt >= 1000 then
    dpt = math.floor(dpt / 1000)
  end

  obj.dpt = dpt
  obj.len = dtlens[ dpt ]
  obj.address = dbobj.address

  if not obj.len then
    alert('invalid data type ' .. obj.address .. ' ' .. tostring(dpt))
    return
  end

  return obj
end

local function initobjects(objects)
  if type(objects) ~= 'table' then
    return
  end

  for addr, obj in pairs(objects) do
    if type(obj) == 'string' then
      obj = { address = obj }
    end

    local dbobj = grp.find(obj.address)
    if dbobj then
      obj = initobject(obj, dbobj)
    else
      alert('missing object ' .. obj.address)
      obj = nil
    end

    objects[ addr ] = obj
  end
end

_M.write = grp.write

_M.setmapping = function(map)
  for _, smap in pairs(map) do
    initobjects(smap.registers)
    initobjects(smap.inputregisters)
  end

  mapping = map
end

return _M

Resident script example:
Code:
local mb = require('user.mbslave')
local mbrtu = require('luamodbus').rtu()

mbrtu:open('/dev/RS485-1', 9600, 'E', 8, 1, 'H')
mbrtu:connect()
mbrtu:setslave('*') -- '*' handles multiple RTU slave IDs

mb.setswap('w')
mb.setfloat16precision(2)

mb.setmapping({
  [1] = {
    coils = {
      [0] = '0/0/1',
      [1] = '0/0/3',
      [2] = '0/0/4',
    },
    discreteinputs = {
      [0] = '1/0/1',
      [1] = '1/0/3',
      [2] = '1/0/4',
    },
    registers = {
      [0] = '1/1/4',
      [1] = '1/1/10',
      [3] = '32/1/6',
      [5] = '32/1/13',
    },
    inputregisters = {
      [0] = '2/1/4',
      [1] = '2/1/10',
    }
  }
})

local gates = {
  ['0/0/3'] = '32/0/1',
  ['1/0/1'] = '32/0/2',
  ['1/0/3'] = '32/0/2',
  ['1/0/4'] = '32/0/3',
}

mb.write = function(addr, value, dt)
  local gate = gates[ addr ]

  if not gate or grp.getvalue(gate) then
    grp.write(addr, value, dt)
  end  
end

while true do
  mb.rtuhandler(mbrtu)
end

In gates table key (left side) is mapped group address and value (right side) is controlling gate object. Write to the given mapped group address will only happen if the gate value is true. Writing to group addresses without a gate group address is always allowed.

RE: Universal Modbus TCP/RTU Slave - imprashant - 22.04.2025

Hi, Thanks for sharing. It is working fine for the coils i.e 1 bit object. But we have holding registers as well that we are using for scene control in which we are sending 0,1 and 2 value from the same group address. How in the above script we can use gate function for the holding registers.

registers = {

      [1] = '6/3/6',
      [2] = '6/0/10',
      [3] = '6/0/11',
      [4] = '6/2/6',-
      [5] = '6/2/7',


   
    },

RE: Universal Modbus TCP/RTU Slave - admin - 22.04.2025

gates table is shared, it works the same for coils and registers.