Gateway Modbus RTU to Modbus TCP

[davidsilva]

Hi,

I have 4 meters connected by Modbus RTU (attachment).

I would like that the Logic Machine works as a Modbus TCP Slave with this 4 meters and with same ID and registers, and then connect to other device. I.e. the Logic Machine works as a Gateway Modbus RTU to Modbus TCP.

Best regards,

[admin]

This is not possible with default Modbus TCP slave as it only supports one slave ID / one set of registers. One solution is to use single slave ID but different registers addresses for each RTU slave.

[EBMel]

Will it be possible to program the LogicMachine so that the meter 1 will use  Modbus TCP slave register 1-100, meter 2 register 101-200 ........?

The Modbus TCP slave exampel only shows register starting from 1.

An exampel/instructions where defined registerts are set would be great!

[admin]

Actual Modbus addressing starts from 0. Documentation for some devices have addressing starting from 1 which creates confusion.

Here's modified slave script where you can specify addresses directly and there can be gaps in register map, for example: 0..15 for meter 1; 100..115 for meter 2 etc.

This script supports 16-bit values only. If only one way communication is needed (Modbus values are read-only) then it can be modified to support 32-bit and 64-bit values internally without additional scripts for splitting values into 16-bit parts.

Code:

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if not mb then   require('luamodbus')   -- list of coil mapping, register mapping and register data types   coils, registers, regdt = {}, {}, {}   -- coil definition   coils[ 0 ] = '1/1/1'   coils[ 1 ] = '1/1/2'   -- register definition   registers[ 0 ] = '2/2/2'   regdt[ 0 ] = dt.int8      registers[ 1 ] = '2/2/3'   regdt[ 1 ] = dt.uint16   -- knx group write callback   function knxgroupwrite(event)     local value     -- try to find matching coil     for id, addr in pairs(coils) do       if event.dst == addr then         value = busdatatype.decode(event.datahex, dt.bool)         mb:setcoils(id, value)       end     end     -- try to find matching register     for id, addr in pairs(registers) do       if event.dst == addr then         value = busdatatype.decode(event.datahex, regdt[ id ])         mb:setregisters(id, value)       end     end   end   -- coil write callback   function mbwritecoils(coil, value)     local addr = coils[ coil ]     if addr then       grp.write(addr, value, dt.bool)     end   end   -- register write callback   function mbwriteregisters(register, value)     local addr = registers[ register ]     if addr then       grp.write(addr, value, regdt[ register])     end   end   -- knx group monitor, handles group writes   busclient = require('localbus').new(0.1)   busclient: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(table.maxn(coils) + 1, 0, table.maxn(registers) + 1, 0)   -- init coils   for id, addr in pairs(coils) do     value = grp.getvalue(addr)     mb:setcoils(id, value)   end   -- init registers   for id, addr in pairs(registers) do     value = grp.getvalue(addr)     mb:setregisters(id, value)   end   -- set callbacks for coil and register write   mb:setwritecoilcb(mbwritecoils)   mb:setwriteregistercb(mbwriteregisters) end -- handle modbus and knx mb:handleslave() busclient:step()