# Multiple tag groups for one modbus device

**URL:** <https://forum.inductiveautomation.com/t/multiple-tag-groups-for-one-modbus-device/41902>\
**Category:** Ignition\
**Created:** [January 2, 2021, 6:00pm UTC](https://forum.inductiveautomation.com/t/multiple-tag-groups-for-one-modbus-device/41902 "2021-01-02T18:00:31Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**Author:** ![Matrix\_Engineering](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/matrix_engineering/32/19781_2.png) [@Matrix\_Engineering](https://forum.inductiveautomation.com/u/Matrix_Engineering)\
**Post date:** [January 2, 2021, 7:06pm UTC](https://forum.inductiveautomation.com/t/multiple-tag-groups-for-one-modbus-device/41902/2 "2021-01-02T19:06:49Z")

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I can’t give you a direct answer to your query but might give some food for thought.

Firstly, are you confusing the actual polling of the tag by the ModbusTCP device driver, with a scan class setting, and the history stored on the tag? If you have a tag with a scan class of 1s, and a ‘default’ (not ‘default historical’) history option enabled on that tag - well, you can only set the history option once, so to have it at both 1 second and 10 seconds you’d need two separate tags, both pointed at the same Modbus register, with two different history settings.

I’ve read a bit about what goes on behind the scenes, a quick search for anything by @k.herron or @p.turmel is always good reading (there are others too of course 🙂 )

e.g. [Using runScript, any effects on Heap Memory - #6 by Kevin.Herron](http://forum.inductiveautomation.com/t/using-runscript-any-effects-on-heap-memory/36682/6)

I feel the answer you may get to this is, there is some level of asynchronous nature, so to guarantee interval specific logging, use transaction groups not historian.

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