Maximum number of registers

[Wo0Zzz]

Hello, 

I'm currently working on a project that is functioning as a sort of gateway. 

I'm reading out a bus and the data is stored as a .txt file on my raspberry. 

The next step is to make this data available for Modbus to readout. 

I'm using the libmodbus library and a example file that I've edited to my needs. 

Everytime there is a data request, it reads all the different .txt files and stores the data in the modbus registers. 

To make it clear I wan't to use different ranges of registers (e.g. a bunch of data on 0x0000 - 0x0010 and 0x1000 - 0x1050 and so on).

Currently I'm only using holding registers, because it only has to store data and don't need to change it. 

I discovered that the max of registers I'm able to create is 125. If I make it bigger i'm getting an error saying, for example: Illegal data address 0x7F in read_registers. And the application is also giving an error: Failed to execute read. 

Is it possible to create more registers, because with my knowledge it is possible to create at least 9999 (and I'm not sure 10000) registers. 

I posted the code on: https://codeshare.io/G7RXdY (only 24Hr available)

Example of the code: https://gist.github.com/JGrossholtz/d1d02a87d535d7772139 

I hope you can help me, otherwise I'm limited to only 124 registers.

Thanks in advance,

Jelle

[Chuck Watson]

From web search:

 

According to the Modbus specification, the limits for one request are:

- read 125 registers

- write 123 registers

- read 2000 bits

- write 1968 bits

 

You just need to do multiple read/write requests to get over these numbers.

 

Chuck Watson BS, CEM, CMVP

Direct USA 724-799-1529

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[Wo0Zzz]

Hi, 

Thanks for your reply. :-)

I was already aware of that. 

That's not my question/issue. 

I do need more registers, if I'm requesting a register in the range of 0 to 124 there is no issue, but if I'm requesting a single register above the 124 'limit' I get this error.

So i'm not requesting more than 125 registers, but need to use more than 125 register slots. 

Is there a limit in the libmodbus library or is there an issue in the particular example I used?

In case of the last, how can I fix that?

Thanks!

Op woensdag 27 januari 2021 om 15:25:13 UTC+1 schreef wat...@gmail.com:

[Wo0Zzz]

Well,

Problem solved, in the original code I used, on line 82, the code creates the number of registers.

Here the author linked to the MODBUS_MAX_READ_REGISTERS, in the modbus.h file it is stated as 125.

That's the reason I couldn't request a register above the 125 limit. Now I used my own number and I can request a register above the 125 limit.

Hope it will help someone else as wel.

Thanks for the help so far.

Jelle

Op woensdag 27 januari 2021 om 16:17:29 UTC+1 schreef Wo0Zzz: