connecting s7-1200 plc to Arduino by Modbus RTU

smsebnaa · Dec 15, 2014

I want to connect s7-1200 (master) to Arduino(slave) by modbus RTU and read its Holding registers.
I connected arduino to Modbus poll software and it's worked! and when one sensor connected to arduino, this software display :
000643-Tx:02 03 00 00 00 02 C4 38
000644-Rx:02 03 04 00 00 00 00 C9 33

000646-Tx:02 03 00 00 00 02 C4 38
000647-Rx:02 03 04 00 11 00 00 99 36

000649-Tx:02 03 00 00 00 02 C4 38
000650-Rx:02 03 04 00 13 00 00 38 F6

00 , 11 , 13 are responses of sensor.
but when I connect PLC to arduino, I got this error : http://cld.persiangig.com/preview/ceUKFGTDtZ/master.jpg

where is the problem?
Tag_REQ is correct?
I should use word or Dword as DATA_PTR?

smsebnaa · Dec 16, 2014

there is no everybody !!!

Archie · Dec 16, 2014

This web site gives a number of examples on interfacing Arduino to a Siemens:

http://program-plc.blogspot.com/search/label/PLC and Arduino

smsebnaa · Dec 16, 2014

Archie said:
This web site gives a number of examples on interfacing Arduino to a Siemens:

http://program-plc.blogspot.com/search/label/PLC and Arduino

in this site, there is not any s7-1200 . I think i should change DATA_PTR, but i don't know how to do it?

JOLTRON · Dec 16, 2014

I have never tried anything like that and I don't know modbus.

But I assume there is documentation for the block (try clicking on the block and pressing F1) and that should give you details about the status / error.

smsebnaa · Dec 16, 2014

I have another error now. MB_Master is always busy and sometimes get error! for example in one minutes there are 1000 times busy and 10 times error. what should i do?
http://cld.persiangig.com/preview/EmIrldWmoU/mb%20master%20master1.jpg

JOLTRON · Dec 16, 2014

You need to determine what the error is to fix it.

I assume that when you have the 'error' bit that the 'status' gives details about what the actual error is.

What is your error? Does the block have documentation that lists all of the errors?

smsebnaa · Dec 16, 2014

JOLTRON said:
You need to determine what the error is to fix it.

I assume that when you have the 'error' bit that the 'status' gives details about what the actual error is.

What is your error? Does the block have documentation that lists all of the errors?

therer is not error but I can not received any response from slave! How do I speed down the modbus? I think this is very faster than slave.

Mike_RH · Dec 16, 2014

Check here to find some examples of MODBUS with the S7-1200:
http://support.automation.siemens.c...d=34677186&lang=en&cspltfrm=0&cssw=0&csbinh=8

Starting with page 747 of the S7-1200 systems manual describes the Load and Master instructions.
You change the baud rate with the Load.

smsebnaa · Dec 16, 2014

Mike_RH said:
Check here to find some examples of MODBUS with the S7-1200:
http://support.automation.siemens.c...d=34677186&lang=en&cspltfrm=0&cssw=0&csbinh=8

Starting with page 747 of the S7-1200 systems manual describes the Load and Master instructions.
You change the baud rate with the Load.

I've seen these site, but there is not any answer. baud rate must be same in master and slave. speed down should done by request (REQ) speed, and I don't know how to do it!

Mike_RH · Dec 16, 2014

Use MB_COMM_LOAD to set baud rate.

m_turk · Dec 16, 2014

In test, you read only 2 words. In s7-1200, you try with 18... Try 1 first.. Than expand...

smsebnaa · Dec 17, 2014

m_turk said:
In test, you read only 2 words. In s7-1200, you try with 18... Try 1 first.. Than expand...

I used baud rate lower and there is no new thing. i should use 2 bytes, but Busy still exist !

smsebnaa · Dec 17, 2014

when i use "P#DB3.DBX0.0 BYTE 2" at DATA_PTR, i must have data block that has 1 word data or seperately bytes? because I want to read one holding register.

JOLTRON · Dec 17, 2014

Mike_RH said:
Check here to find some examples of MODBUS with the S7-1200:
http://support.automation.siemens.c...d=34677186&lang=en&cspltfrm=0&cssw=0&csbinh=8

Starting with page 747 of the S7-1200 systems manual describes the Load and Master instructions.
You change the baud rate with the Load.

Was this link supposed to be to a manual? for me it just shows a list of support pages with nothing in the search fields.

connecting s7-1200 plc to Arduino by Modbus RTU

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