LM as Modbus Slave. datatype and offset

[ikhy]

Hi! I ask for your help, I am a beginner.
I am using LM as Slave via script.

When I try to write an integer value in my PLC to an integer register (uint16 in LM), I cannot do it. But if I write a floating point value to this register, then an integer value is written.
When I test in Modbus Poll, I have the status “illegal data address” Slave LM.

is it an offset problem? What should I do?

[Daniel]

It might help if you show us the slave script.

[ikhy]

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','1/1/3' ,'1/1/4' }

  -- list of register mapping, starting from 0
  registers = { '3/1/1', '3/1/2'}

  -- list of register data types, element count must match registers table
  regdt = { dt.uint16,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('хх.хх.хх.хх', 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:step()

---

changed nothing

[Daniel]

You have done everything correct here. I assume the objects 3/1/1 and 3/1/2 are 2 byte unsigned integer?

[admin]

Which address are you using from ModBus side? You can only use 0 and 1 because you have 2 registers defined.

[ikhy]

Which address are you using from ModBus side? You can only use 0 and 1 because you have 2 registers defined.

yes. use 0 and 1 registers

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immediately after connecting to LM

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and I can write data from Modbus Poll. But from one type PCL i can not. and from other type PLC I can only when I write float

---

You have done everything correct here. I assume the objects 3/1/1 and 3/1/2 are 2 byte unsigned integer?

yes

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I think maybe my controller starts reading not from 0, but from 16 bits. therefore, he understands part of the float as integer. And i need to do offset. is it possible?

[ikhy]

please, can you test this script in some Modbus Server? do you get an "illegal data address" too?

"illegal data address" : The data address received in the query is not an allowable address for the server (or slave). More specifically, the combination of reference number and transfer length is invalid.

[Daniel]

This script was used in many projects and nobody had this issue. Try reading register 1.

[ikhy]

yes-yes! i totally agree with you. i see how many people use it. i only want to understand where is my issues. i can read and write values via modbus server but with errors.

[Daniel]

The issue is somewhere in config of your PLC.
PS. LM is modbus server here, your PLC is client.

[ikhy]

The issue is somewhere in config of your PLC.
PS. LM is modbus server here, your PLC is client.

yes! it was PLC issues. Thank you for the help!