# Modbus TCP Addressing issue

**URL:** <https://forum.inductiveautomation.com/t/modbus-tcp-addressing-issue/15701>\
**Category:** Ignition\
**Created:** [October 18, 2017, 1:20pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-addressing-issue/15701 "2017-10-18T13:20:38Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![pascal](https://avatars.discourse-cdn.com/v4/letter/p/e9a140/32.png) [@pascal](https://forum.inductiveautomation.com/u/pascal)\
**Post date:** [October 18, 2017, 1:20pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-addressing-issue/15701/1 "2017-10-18T13:20:38Z")

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Hello,  
I need some help with modbus addressing.  
We have a device installed on a site and we would like to retrieve data from this device. Here is the address table :  
 ![](https://us1.discourse-cdn.com/inductiveautomation/original/2X/c/c41dfb56e4ac6c246e9d1d6a9f16eb2790ed863e.png)  
We only have 3 registers to read but I can’t figure out how to manually create the addresses.  
Any help ?

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**Author:** ![oscar.salcedo](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/oscar.salcedo/32/11019_2.png) [@oscar.salcedo](https://forum.inductiveautomation.com/u/oscar.salcedo)\
**Post date:** [October 18, 2017, 2:44pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-addressing-issue/15701/2 "2017-10-18T14:44:54Z")

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Hello Pascal,

I would start on the documentation here:  
[https://docs.inductiveautomation.com:8443/display/DOC79/Modbus+Addressing](https://docs.inductiveautomation.com:8443/display/DOC79/Modbus+Addressing)

Modbus addressing can be tricky; you have to know the datatype of the source address, any scaling that would need to be applied to the tag once configured in Ignition, the device ID, and any potential offsets on the Holding Registers.

For example, you could try to create a tag of Float datatype for your flow sensor, and pointing to 1.HR4 and see if it returns the desired value.

Cheers,

Oscar.

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**Author:** ![hamlinjr](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/hamlinjr/32/8228_2.png) [@hamlinjr](https://forum.inductiveautomation.com/u/hamlinjr)\
**Post date:** [October 19, 2017, 10:02pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-addressing-issue/15701/3 "2017-10-19T22:02:15Z")

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Pascal,  
Based on the datatypes and length shown on your table, it appears you need 32bit Modbus designators. Following the link and details provided by Oscar, I would try the following and see what you get (assuming a Mddbus ID of 1);

- 1.HRF4
- 1.HRUI6
- 1.HRF40

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<div class="post-metadata">

**Author:** ![pascal](https://avatars.discourse-cdn.com/v4/letter/p/e9a140/32.png) [@pascal](https://forum.inductiveautomation.com/u/pascal)\
**Post date:** [October 23, 2017, 9:03am UTC](https://forum.inductiveautomation.com/t/modbus-tcp-addressing-issue/15701/4 "2017-10-23T09:03:45Z")

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We found out the solution to our problem.  
We had to toogle the propertie “Reverse Word order” in the device’s parameters.  
The adresses 1.HRF4, 1.HRUI6, 1.HRF40 work fine.  
Thanks