# Tags register address

**URL:** <https://forum.inductiveautomation.com/t/tags-register-address/27306>\
**Category:** Ignition\
**Created:** [August 9, 2019, 7:41am UTC](https://forum.inductiveautomation.com/t/tags-register-address/27306 "2019-08-09T07:41:29Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![miculacristianradu](https://avatars.discourse-cdn.com/v4/letter/m/b782af/32.png) [@miculacristianradu](https://forum.inductiveautomation.com/u/miculacristianradu)\
**Post date:** [August 9, 2019, 7:41am UTC](https://forum.inductiveautomation.com/t/tags-register-address/27306/1 "2019-08-09T07:41:29Z")

</div>

Hi,

I have a question regarding the way we set tag values in Ignition.  
I noticed that every group of tags, when we set the register address,beside the number it has different letter on prefix. (see bellow)

 ![tag1](https://us1.discourse-cdn.com/inductiveautomation/original/2X/6/6d2a6dda1a28c43b655bbbdad235f5da984b52b8.jpeg)  
 ![tag2](https://us1.discourse-cdn.com/inductiveautomation/original/2X/4/4dd47c7a420e148d2a765e3778f703a13a936ab3.jpeg)  
 ![tag3](https://us1.discourse-cdn.com/inductiveautomation/original/2X/c/c88649d74675576ec30ac987db3430597ac7aaca.jpeg)

Here it’s the list with registers addresses:

 ![list](https://us1.discourse-cdn.com/inductiveautomation/original/2X/9/946999c8049670747ff859a4a70332fe1bb9bbb1.jpeg)

How we can know what letter to put on preffix, if the list we get from PLC programmer contains only number for registers?

Thank you!

---

<div class="post-metadata">

**Author:** ![JordanCClark](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/jordancclark/32/83362_2.png) [@JordanCClark](https://forum.inductiveautomation.com/u/JordanCClark)\
**Post date:** [August 9, 2019, 11:54am UTC](https://forum.inductiveautomation.com/t/tags-register-address/27306/2 "2019-08-09T11:54:35Z")

</div>

This may help explain things:

[https://docs.inductiveautomation.com/display/DOC79/Modbus+Addressing](https://docs.inductiveautomation.com/display/DOC79/Modbus+Addressing)

---

<div class="post-metadata">

**Author:** ![miculacristianradu](https://avatars.discourse-cdn.com/v4/letter/m/b782af/32.png) [@miculacristianradu](https://forum.inductiveautomation.com/u/miculacristianradu)\
**Post date:** [August 20, 2019, 10:11am UTC](https://forum.inductiveautomation.com/t/tags-register-address/27306/3 "2019-08-20T10:11:33Z")

</div>

Thanks!