Modbus Addressing

TahirQ · May 26, 2013

If I have to write an input on Discrete I/O module on Modicon M340 PLC , I know I can use %I.

Now I have to use modbus and read some additional inputs from another device other than the one on the module.How shall I write their addresses on the modules?
Also what is the proper adrdressing format of inputs you want to read through modbus?

dipesh9486 · Jun 15, 2013

You can't write directly I/O to the plc you can use memory bits to read or write the I/O
Adresses are following :-
Inputs:- 400001.0, 400001.1, 400001.2.......
Registers:- 400001, 400002...
you can use this...

GeoffC · Jun 15, 2013

You need to map the @I and %Q bits to bits of a memory word. The addressing of the memory words in an M340 is %MW. You can write each bit one rung at a time, for example

----| |--------( )
%I1.0 %MW1.0
Or you can use the Bit_To_Word instruction to write 16 bits at a time
In modbus the %MW words may be addressed as 40000 style numbers, just note there is a one offset in the address as %MW starts at 0 and in modbus the first address is 40001 (%MW0 = 40001)

You can also use the %M memory bits (you will still need to use code to map the %I to a %M bit)
In modbus these bits are addressed as 10000 numbers (%M0 = 10001)

Note some Modbus drivers do use the IEC format %M and %MW

hope this helps

V0N_hydro · Jun 15, 2013

Can't you use the read coils modbus command to read the inputs?
address range 10000?

GeoffC · Jun 15, 2013

No - with the M340s and the Unity based Quantums, the Modbus 10000 addressing is mapped to the %M memory bits, not to the %I addresses that are used by the plcs to address the inputs

dipesh9486 · Jun 16, 2013

If you want to map the %m adressing via modbus the adressing would be as per followig

%m0, %m1, %m2= 000001, 000002, 000003
You can't use 10000 because it has only the read only adress and it is not available in the modbus map...

Good Luck...

V0N_hydro · Jun 17, 2013

somehow the Magelis HMI is able to read the %I addresses from the M340 PLC without them being mapped to %M

I note that the magelis simulator in vijeo designer can't read them from the unity M340 simulator, but the magelis simulator can read from the M340 PLC.

GeoffC · Jun 18, 2013

There are non standard extra function codes used by companies to perform non standard functions - for example programming a plc over a modbus link. These extra functions are generally not documented and are not supported by the standard drivers. I guess the Magelis is using some of this expanded functionality

marcolino76 · Dec 5, 2019

Hello I read your info about modbus addressing with %MW register.
I have a PLC with registers
PLC ADDR: MW4513 and the machine constructor write MODBUS ADDR: 44514
If I read the value with TCP modbus i read the exactoly value on the address 4513 Modbus ( 1st byte ) and I don't understand why.
Then I need to write 1 in the 7th bit of %MW10100 from my supervisor software, but if I make an or in the 10100 modbus adr or 50101 ( 10100 + 40001 ) it doesn't work.

Can someone hel me please ?
Thanks

Firejo · Dec 5, 2019

Tacking on to the end of someone else's thread is frowned upon plus this thread is over 6 years old so a lot of people will ignore it. You need to start your own thread with your question.
Good luck.

Lare · Dec 5, 2019

As Firejo stated you should start new thread for this.

%MW10100 is on so called extended memory area on modbus. Originally modbus had 9999 registers. and numbering was 40001 to 49999.
Then there is extended addressing, which is 10000 and over addressing.
But it isn't 50000 as modbus have only 0X,1X, 3X and 4X starting addressing.
Adresses from 10001 starts from 410001 which is %MW10000 on Schneider CPU.
So %MW10100 is finded from modbus 410099 address

And %MW1100 is 41099 address, but it can also writed 401099 on extended addressing
%MW0..%MW9999 can be 5 or 6 numbers on modbus
%MW10000 and over is allways 6 numbers on modbus

marcolino76 · Dec 5, 2019

Yes ok I will starta new thread. Thanks a lot for the quick reply.
Thanks

Modbus Addressing

TahirQ

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dipesh9486

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GeoffC

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V0N_hydro

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GeoffC

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dipesh9486

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V0N_hydro

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GeoffC

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marcolino76

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Firejo

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Lare

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marcolino76

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