# MODBUS RTU RS485 Adress how to write

**URL:** <https://forum.inductiveautomation.com/t/modbus-rtu-rs485-adress-how-to-write/79746>\
**Category:** Ignition\
**Created:** [September 27, 2023, 6:26pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-rs485-adress-how-to-write/79746 "2023-09-27T18:26:57Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Thierry\_HOARAU](https://avatars.discourse-cdn.com/v4/letter/t/a5b964/32.png) [@Thierry\_HOARAU](https://forum.inductiveautomation.com/u/Thierry_HOARAU)\
**Post date:** [September 27, 2023, 6:26pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-rs485-adress-how-to-write/79746/1 "2023-09-27T18:26:57Z")

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Hello Dear, how to correctly write :  
S30x0008 holding register in modbus Ignition adress ?  
Ty ! for help

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**Author:** ![andrews](https://avatars.discourse-cdn.com/v4/letter/a/898d66/32.png) [@andrews](https://forum.inductiveautomation.com/u/andrews)\
**Post date:** [September 28, 2023, 3:44am UTC](https://forum.inductiveautomation.com/t/modbus-rtu-rs485-adress-how-to-write/79746/2 "2023-09-28T03:44:35Z")

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Check out this and let me know if it helps.

[https://docs.inductiveautomation.com/display/DOC81/Modbus+Address+Mapping](https://docs.inductiveautomation.com/display/DOC81/Modbus+Address+Mapping)

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<div class="post-metadata">

**Author:** ![Thierry\_HOARAU](https://avatars.discourse-cdn.com/v4/letter/t/a5b964/32.png) [@Thierry\_HOARAU](https://forum.inductiveautomation.com/u/Thierry_HOARAU)\
**Post date:** [September 30, 2023, 12:15pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-rs485-adress-how-to-write/79746/3 "2023-09-30T12:15:43Z")

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Hello Dear , I found that there is +1 offset  
as my adress resgister is 00 for voltage for example correct floating value is 1  
as I add +1 for all register values its OK  
PS : before converting HEX to DEC  
thanks a lot

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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:** [September 30, 2023, 7:21pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-rs485-adress-how-to-write/79746/4 "2023-09-30T19:21:20Z")

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There is a setting in the driver for one based/zero based, go to edit settings and click show advanced.

Therefore your registers in your address can match the documentation.