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

Hello, first of all, thank you very much for
 the patience you have with me and with this
 modbus question.
I have tried to change the way of
 communicating.
 I have tried now that the plc is 
master and write in my external device, 
which I have programmed as a slave ... but
 the error continues, as I mentioned before. 
 As you say I have reviewed the port and I have 
placed the port that Tia Portal hardware
 indicates to me ..... in fact I have not
 written it but I have clicked on the
 possibilities of the menu and in this 
menu I have chosen the port that corresponds
 to the PTP module that I have connected.
 I have checked that this port is the same 
one that comes in the constants table of
 the system as in the DB of the 
modbus _comm_load and also in the hardware
 configuration of Tia Portal that is the port
corresponding to the physical communication
 module that I have connected to the CPU
 as you can see in the PDF the three 
coincide is the port 263.. The cpu error 
disappears if I stop calling mdbus_master 
from ob1. Therefore it seems that the error
 is within this block

so I am very confused and I do not know how .

Thanks for the help you are giving me

It's false. That wants to say that itis not

being executed, I suppose ...  The block is called only once because it is in OB1 but it is called by bool "first scan". There is something

more to tell you; when I "erase" or stop calling

the modbus master module in OB1, the error in the

CPU disappears ..... .Thank you

Sorry...It is true. I appreciate it, but when

I click on the link you sent me:

https://support.industry.siemens.com/tf/ww/en/posts/problem-modbus-rtu-et200sp-as-eslave/How%20do%20you%20evaluate%20the%20status%20of%20system%20blocks% 20in% 20STEP% 207% 20 (TIA% 20Portal)?

 I get this: 

Thanks

Kaulquappe

Sorry, I didn't insert the correct link. Second try:

How do you evaluate the status of system blocks in STEP 7 (TIA Portal)?

Hello

I have read several posts from people who have encountered this same problem. In my case, as in them, the parameters of parity, bit stop, speed ... etc are fine. I have also checked the connection cable and exchanged TX RX, I have checked the parameter Line_Pre ... etc I am learning to use the previous library (SaveStatus ") and I run into a problem. As I understand in the siemens support page, the link takes me to a website where the status status parameter is analyzed, like a 4-byte array. However the FB "SaveStatus", contained in the library that is downloaded from this page has an array of 10 DWord. I guess they are different things. I am analyzing the elements of the DB array corresponding to the "SaveStatus" of the master, but I do not know what part of the communication corresponds to each element of the array to be able to locate where the error is affecting. In the help of Tia Portal does not speak to me about this FB "SaveSTatus". Is there a page that explains what each element of the 10 in this array represents?

Thank you

Hello everyone

Finally I have been able to solve (more or less; not completely) the issue of communication, but it works. I share my solution here in case it is useful for someone:

The ModbusCommLoad block is called in the first scan cycle with the parameterization of the serial communication. The ModbusMaster is called in a cyclic ob. To write several analog values ​​from my PLC ("master") to the other device (slave), I use an auxiliary program, so that, in communication, I ignore errors 16 # 81E2 16 # 81E7. Both errors appear at the beginning of each communication. I have not been able to disappear, I have changed the connection cable, I have isolated the "GND" well, checked the connection parameters ... etc. The values ​​are sent from a DB with access not optimized in the form of words, one by one through an auxiliary program that "sweeps" all the records to be sent, cyclically, to send only 1 word at a time. When I tried to send more, to me personally, problems have arisen.

In this way, finally, my modbus connection works (with some limitations, especially in time, because it sends the records cyclically, one by one), but it works for me and the slave reads well what my PLC sends.

Thanks to all who have helped me

Regards

Hello!

I have rhe same problem. Could you please share the solution?

thanks,

BR.