Hi,

I'm using a S7-1200 with a CM1241 for read the data from a Modbus RTU slave.

I have the register layout from the slave (attached), but I don't know how to use it with DATA_ADDR and MODE parameters from the instruction MB_MASTER :

https://support.industry.siemens.com/cs/ww/en/view/107623221/69788292875

In the register layout, we can see that the register start at the address 0000 to 0037.

And I want to read the address 0000 "Nombre d'impulsions : entrée 1" and for that, I need to use the modbus function 04 (Read Input Registers).

But when I read the table DATA_ADDR and MODE parameters, if I want the modbus function 04, the address need to start at the address :30001 

I'm lost and confused.

Did someone already create a connection like this ?

Thank you,

Luc

Assuming that you have understood the task correctly, "read input register at address 0000", then you should be able to use the notation (3)0001 to read the slave/server Input register 0000.

Addressing notation that uses leading numeral and decimal numbering is one-based addressing that gets converted internally to zero-based addressing that Modbus expects.

OT Metric / Leading numeral notation / Modbus message
0000                      (3)0001                           0x00
0002                      (3)0003                           0x02
0004                      (3)0005                           0x04

Make sure you read at least 2 registers to get the full 32 bits.
 

Hi Danw,

Thank you for your reply, 

I understand the notation that you give me, but I'm not sure how to convert this notation to the two entry of the "MB_Master_DB" : MODE and DATA_ADDR:

unknown user

 The MB_MASTER instruction uses a MODE input rather than a Function Code input. The combination of MODE and Modbus address determine the Function Code that is used in the actual Modbus message. The following table shows the correspondence between parameter MODE, Modbus function code, and Modbus address range.

So if I want to access to the notation : (3)0001, 

I need to use the MODE: 0

And DATA_ADDR : 30001 ?

But I have no data return.

For the buffer return, I have a Array [0..5] if UInt.

EDIT :

It's working !

I put a wrong parameter in the DATA_LEN, 

The format type is in Word and I was thinking that's in Bit. 

Result : the LEN was too big and my slave didn't answer.

Good parameters are:

MODE: 0 

DATA_LEN: 8 (for read the 8 counters)

DATA_ADDR: 30001

Thank you again,

Luc