Dear all,

I have a problem regards the modbus Tx message. I was using S7-416H CPU and ET200SP with CM PtP, the modbus communication was setup through CM PtP. I want to read the current measurements of the 3-phase power meter, so I use FB640 and FB641 for programming.

Inputs are as shown in the attached zip file . 

I couldn't get any reply from the power meter, and when I use another to check the message sent, I found the message sent out was "7a df ff ff bf 1d 1e ff". But in my program, the message supposed to be sent out should be "0b 04 75 31 00 20 xx xx". 

I couldn't find the reason. Can anybody help?

BTW, where can I check the help file of the Modbus library FBs such like FB640, FB641 and FB642? I couldn't find it through the Simatic help file.

Thanks for the help.

Image file 2

kevinlin_5

Dear all,

I have a problem regards the modbus Tx message. I was using S7-416H CPU and ET200SP with CM PtP, the modbus communication was setup through CM PtP. I want to read the current measurements of the 3-phase power meter, so I use FB640 and FB641 for programming.

Inputs are as shown in the attached image file (I have 4 image files, so I will post the other 3 in the replies below, sorry for the inconvenience caused, as I couldn't attach more than one image files in a single reply). 

I couldn't get any reply from the power meter, and when I use another to check the message sent, I found the message sent out was "7a df ff ff bf 1d 1e ff". But in my program, the message supposed to be sent out should be "0b 04 75 31 00 20 xx xx". 

I couldn't find the reason. Can anybody help?

BTW, where can I check the help file of the Modbus library FBs such like FB640, FB641 and FB642? I couldn't find it through the Simatic help file.

Thanks for the help.

 Hello, Duris,

Thank you for the suggestion. I forgot about zipped file. 

Duris_I

Hello,

sry only recommendation you can zip screenshots and attach zip here. Pay attention to max size of attached file.

Hi, Duris,

Thanks for the recommendation.

Yes, I have tried with PC application directly connected to the power meter. It works perfectly. Message sent by the PC application was what I said in my main post, "0b 04 00 00 00 20 xx xx". I didn't know why the data address here was 00 00, maybe it's beacuse it was set to 'INPUT REGISTER' in the PC application. 

I have also tried to change the data address to 0000 in my program, but it even did not send any message. If I changed back to 7531, it sent message, but the message sent was "7a df ff ff bf 1d 1e ff".

Hello, Duris,

Thanks for the reply.

In my program, the data address was set correctly. I'm reading 20 words starting from the data address 30001. The problem is when I monitor the data sent, it was "7a df ff ff bf 1d 1e ff". The first byte '7a' was the MB address, and in my application, it should be '0b', which I enter at the input 'MB_Addr'  of FB641. The second byte 'df' was the function code, and it should be '04', which I manually set by move the value to the instance datablock of FB640.

I didn't get any reply from the power meter. I guess it's because of the sent message not correct. But I don't know why the message sent is not as expected.

Hope someone may have an idea about this.

Thanks.