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:

1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586

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()

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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

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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!