Hi all

I would be very grateful if you could help me in this matter. I have an et200sp (s1510) and I want to read some of its analog values ​​from an external device that supports modbus rtu communication. I have many doubts and, of course, what I have tried does not work. I am not familiar with modbus although I have read the siemens forum documentation, but some things I still do not understand. In my plc, in ob100 I have programmed the mb_comm instruction and in OB1 the mb_slave. My external controller has configured it as a master (since it has a small scada where I will display the data of the PLC and I have configured the serial communication data (bit, speed, bit stop ...) The interface of the external controller is simple, apart from the serial parameters, it only asks for the address of the modbus slave (my plc), the mode of operation (my plc is a slave) and the modbus address of each record to be read (here's my problem)

I have two important questions: 1) My external device asks me for the address (modbus) of each record to be read. Where do I find that address? I have read that DW0 would correspond to 40001 for the external "reader" master. It is right?

2) Since the et1500sp is a slave, it is not necessary to program the mb_master in any part of the plc program, it would only write the mb_slave, is it correct?

Thank you very much for the help

Kaulquappe

"does not work" is no proper error description. Which error do you get?

You are absolutely right, it is important 
to explain the issues well. The system does 
not work because the master gives me an error
 message (with a code of this device), but as
 you say I will find the error codes and status 
of the outputs of the blocks and show them
 in this post .

Before continuing I would appreciate it if 
you could resolve a question: I have been 
looking at this document https://support.industry.siemens.
com/cs/ww/en/view/68202723.

I do not understand why the shape of the 
blocks is not the same as the one I have in
 my Tia Portal project. I see the slave block
 as a different FB than it does in my project
 when I call from the library. Is it because 
in this project it is particularly done like 
this? . Is it firmware issue? Some parameters 
of the blocks look different. I can work n
ormally with the blocks of the library 
(those of my project, look in the image 
the slave block on the right, is different f
rom the one on the left)

Thank you

Hello

I'm repeating the program again. 
First of all thanks for the help .... Regarding
 the modbus addresses, we have said 
that DW0 of the plc corresponds to 
the address modbus 40001, my question is:
 is the order correlative? 
That is, DW1 would be 40002 Dw3 would be 40003 ...
 because if so, I do not understand why the 
last record of modbus correponde to 49999, 
being the last Dword DW1998.
​Could you read records stored in a DB?

My other question is: what are the
 records of the array of the photo?
 They belong to DB_slave. Are they related
 to the data that will be read by the
 external master using Modbus?

Thank you

cesarinko

 the modbus addresses, we have said 
that DW0 of the plc corresponds to 
the address modbus 40001, my question is:
 is the order correlative? 
That is, DW1 would be 40002 Dw3 would be 40003 ...
 because if so, I do not understand why the 
last record of modbus correponde to 49999, 
being the last Dword DW1998.
​Could you read records stored in a DB?

 DW0 reserves 4 bytes, so the nex DW you can define is DW4, NOT DW1. DW1 will overlap with DW0, and create problems. As it is a Double Word, it contains 2x Words, and each Word contains 2x Bytes.

It is true, I understand what you tell me 
about the Words size, if we define a word, 
the next word should go 2 bytes later and
 if it is DWord 4 bytes later. Excuse me, do
 not explain me well.

I ask it in another way. If, for example,
 the DW0 is 40001 in modbus, the DW4 would 
be 40002 the DW8 40003 and so on?

Thank you

This is error 16 # 8282. I have searched 
and the documentation says that the module 
"is not available". I checked the PORT entry
 and placed the port the program gives me for
 the module. This time I have programmed the
 common in OB1 calling him in the first scan.

I attach error images and blocks in case
 someone can help me.

Thank you

Hello

Thank you very much for the information. 
I have studied it and it helps me understand
 a little more. But I could not make the 
connection in a satisfactory way. I have 
repeated the program again, this time with
 my external device as a slave so that the
 ET200SP PLC "writes" the values ​​in the 
external device (instead of the external one
 being a master and reading from the PLC as
 a slave). I have configured the blocks as 
I think they should be and at the moment of
 sending them to my PLC the CPU goes into
 error. The error is caused by the master 
module, because if I isolate it and I do 
not call it from OB1, the error disappears
. According to the diagnostic buffer "there 
is access problem to read the data from the
 periphery" I have reviewed everything many 
times but I can not find the error. 
The buffer says: "error in read access to 
the periphery (address I 0) in FB 613"

I would like to ask if someone can tell 
me if this error that I read in the cpu 
corresponds to a bad programming of my 
blocks or refers to the external device 
(whose parameters for modbus rtu are very
 easy to program). I am not able to continue
 in this work. The buffer diagnosis says:

"Error in reading access to the periphery (address I 0) in FB 613"

Thank you