# Show some interesting things about s7-1200 PLC communication

**URL:** <https://discourse.nodered.org/t/show-some-interesting-things-about-s7-1200-plc-communication/87604>\
**Category:** Industrial\
**Created:** [30 April 2024 07:03 UTC](https://discourse.nodered.org/t/show-some-interesting-things-about-s7-1200-plc-communication/87604 "2024-04-30T07:03:27Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![benefit\_union](https://avatars.discourse-cdn.com/v4/letter/b/ba9def/32.png) [@benefit\_union](https://discourse.nodered.org/u/benefit_union)\
**Post date:** [30 April 2024 07:03 UTC](https://discourse.nodered.org/t/show-some-interesting-things-about-s7-1200-plc-communication/87604/1 "2024-04-30T07:03:27Z")

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![20240430144931](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/b/0/b0da84e3707c31a0111b60cca15b8b727d02a3d0.png)  
 ![20240430144953](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/d/a/da9a228f0f1f0a36f17b54acae25480ae50da717.png)  
 ![20240430145000](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/6/9/6901843b961d87dda9636c8ee011f5f48f2a9ed8.png)  
 ![20240430145007](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/c/1/c14d61833cdd0a15980819b0bc6aef78ba8794f9.png)  
I use node-red-contrib-s7 to communicate one S7-1214C PLC .But I write wrong address length at DB6001,S1556.30 and there show error message in node-red .  
OK , there two questions .  
First :  
I also write wrong address like DB6001,S1466.100 and the right address is DB6001,S1466.30.But NODE-RED not show error message.  
Second question:  
AND NODE-RED show error message address is DB6001,R1536 .But this address is valid.  
Hope this help U like me do this communication !  
 ![20240430145609](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/5/0/501d652e4571d6d06304034a74ed097a43dd359f.png)

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**Author:** ![OriolFM](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/oriolfm/32/30710_2.png) [@OriolFM](https://discourse.nodered.org/u/OriolFM)\
**Post date:** [30 April 2024 08:15 UTC](https://discourse.nodered.org/t/show-some-interesting-things-about-s7-1200-plc-communication/87604/2 "2024-04-30T08:15:23Z")

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Can you check the absolute offset using cross-reference? I see that the struct where the number is is not the first one in the list, and it may have a different offset than the one you can see in the list.

 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/f/d/fdb49f1c4a6d9970f1c75ed36d9e5e818842ee0e.png)

As you can see in the previous picture, the offset listed next to the variable is relative to the struct, not the absolute offset in the DB. But if you check in cross-reference (or properties) you can get the absolute offset value for the DB.

It could be that the variable where you don't get an error has actually the right offset, and the one you think is right but don't get an error is actually wrong.

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**Author:** ![benefit\_union](https://avatars.discourse-cdn.com/v4/letter/b/ba9def/32.png) [@benefit\_union](https://discourse.nodered.org/u/benefit_union)\
**Post date:** [30 April 2024 09:12 UTC](https://discourse.nodered.org/t/show-some-interesting-things-about-s7-1200-plc-communication/87604/3 "2024-04-30T09:12:39Z")

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Yes,I shortcut offset address is absolute address in DB data, and I have right data from node-red to PLC . I want upload picture but network not good .  
Thanks for your advice.

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**Author:** ![KarolisL](https://avatars.discourse-cdn.com/v4/letter/k/a4c791/32.png) [@KarolisL](https://discourse.nodered.org/u/KarolisL)\
**Post date:** [30 April 2024 15:33 UTC](https://discourse.nodered.org/t/show-some-interesting-things-about-s7-1200-plc-communication/87604/4 "2024-04-30T15:33:54Z")

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> [@benefit\_union](#):
>
> AND NODE-RED show error message address is DB6001,R1536 .But this address is valid.  
> Hope this help U like me do this communication !

I think what it has to do is that, s7 node sets translation of all tags of your connection, meaning if one of tags is unavailable whole batch of variables is regarded as bad and that's why you get an error.

> [@benefit\_union](#):
>
> I also write wrong address like DB6001,S1466.100 and the right address is DB6001,S1466.30.But NODE-RED not show error message.

If your defined variables are in range of your DB you can point to any memory area and will get some kind of result, but it might look like gibberish. No error in this case

Your variables definitions allow received buffer of values to be parsed in correct format.

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**Author:** ![benefit\_union](https://avatars.discourse-cdn.com/v4/letter/b/ba9def/32.png) [@benefit\_union](https://discourse.nodered.org/u/benefit_union)\
**Post date:** [1 May 2024 08:18 UTC](https://discourse.nodered.org/t/show-some-interesting-things-about-s7-1200-plc-communication/87604/5 "2024-05-01T08:18:27Z")

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Good.  
You give me the right answer.  
Thank U very much!

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**Author:** ![system](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/1X/d073cd938eafa2e558d7c2cd59003b3ef4963033.png) [@system](https://discourse.nodered.org/u/system)\
**Post date:** [15 May 2024 08:19 UTC](https://discourse.nodered.org/t/show-some-interesting-things-about-s7-1200-plc-communication/87604/6 "2024-05-15T08:19:11Z")

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