# Could not read/write registers (Wago 750-880, Modbus)

**URL:** <https://forum.inductiveautomation.com/t/could-not-read-write-registers-wago-750-880-modbus/16148>\
**Category:** Ignition\
**Created:** [November 28, 2017, 5:07pm UTC](https://forum.inductiveautomation.com/t/could-not-read-write-registers-wago-750-880-modbus/16148 "2017-11-28T17:07:54Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![elena](https://avatars.discourse-cdn.com/v4/letter/e/278dde/32.png) [@elena](https://forum.inductiveautomation.com/u/elena)\
**Post date:** [November 28, 2017, 5:07pm UTC](https://forum.inductiveautomation.com/t/could-not-read-write-registers-wago-750-880-modbus/16148/1 "2017-11-28T17:07:54Z")

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Hello,

I have a few tags in the Tags section of Ignition Designer. I can read physical I/O and read/write coils.  
However, I am not able to read/write holding registers. For example, I want to read an integer variable that is declared in PLC program with address %MW0. According to [Wago manual](http://www.wago.us/appnoteadmin/appnotes/a300003/public/a300003_en%20-%20Modbus%20with%20WAGO%20Ethernet%20Couplers%20and%20Controllers.pdf) (p.58) this address corresponds to Modbus address 12288. I tried the following paths:

[Wago]HR12288 - invalid address  
[Wago]HR768 - no result  
[Wago]HR769 - no result  
[Wago]C12289 - reading first bit

I would appreciate if you can provide some guidance on the issue.

Thanks.

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**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\
**Post date:** [November 28, 2017, 5:09pm UTC](https://forum.inductiveautomation.com/t/could-not-read-write-registers-wago-750-880-modbus/16148/2 "2017-11-28T17:09:38Z")

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> [@elena](#):
>
> HR12288

Did you try HR12289?

Are there errors on the console or does the device just not respond?

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<div class="post-metadata">

**Author:** ![elena](https://avatars.discourse-cdn.com/v4/letter/e/278dde/32.png) [@elena](https://forum.inductiveautomation.com/u/elena)\
**Post date:** [November 28, 2017, 5:12pm UTC](https://forum.inductiveautomation.com/t/could-not-read-write-registers-wago-750-880-modbus/16148/3 "2017-11-28T17:12:40Z")

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Yes. In this case system marks tag with red and sets the value to null.

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<div class="post-metadata">

**Author:** ![elena](https://avatars.discourse-cdn.com/v4/letter/e/278dde/32.png) [@elena](https://forum.inductiveautomation.com/u/elena)\
**Post date:** [November 28, 2017, 5:14pm UTC](https://forum.inductiveautomation.com/t/could-not-read-write-registers-wago-750-880-modbus/16148/4 "2017-11-28T17:14:35Z")

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Sorry, my bad. HR12289 works. Thanks for your help 🙂

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<div class="post-metadata">

**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\
**Post date:** [November 28, 2017, 5:18pm UTC](https://forum.inductiveautomation.com/t/could-not-read-write-registers-wago-750-880-modbus/16148/5 "2017-11-28T17:18:04Z")

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If you find all your addresses are offset by 1 like this, you can try setting the “one-based addressing” advanced property for your device to false.