# Modbus TCP Addressing

**URL:** <https://forum.inductiveautomation.com/t/modbus-tcp-addressing/56861>\
**Category:** Ignition\
**Created:** [March 4, 2022, 7:45pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-addressing/56861 "2022-03-04T19:45:52Z")\
**Posts on this page:** 9\
**Page:** 1

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**Author:** ![Jatin\_Kumar\_Singh](https://avatars.discourse-cdn.com/v4/letter/j/87869e/32.png) [@Jatin\_Kumar\_Singh](https://forum.inductiveautomation.com/u/Jatin_Kumar_Singh)\
**Post date:** [March 4, 2022, 7:45pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-addressing/56861/1 "2022-03-04T19:45:52Z")

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Hi, I am trying to access the following tag in Ignition. Got it connected via Modbus TCP driver.

Details of the tag:-

Unit ID - 1  
Register Offset - 240  
Bit No. - 0  
Holding Register - 40241  
Format- f

I am using the following tagpath to access this. The quality of the tag is good but I am getting 0 as the output which is not the correct value.

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/a/3/a3cd59f5d4377b859406597eee6bebc157e8f764.png)

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<div class="post-metadata">

**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [March 4, 2022, 7:51pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-addressing/56861/2 "2022-03-04T19:51:28Z")

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Get rid of the “F” when accessing bits. Use `[Elrest]1.HR241.0`.

Or if you really want the whole floating point value spanning HR241 and HR242, use `[Elrest]1.HRF241`. You may have to configure word swapping if the value is scrambled.

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<div class="post-metadata">

**Author:** ![Steve\_Laubach](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/steve_laubach/32/60900_2.png) [@Steve\_Laubach](https://forum.inductiveautomation.com/u/Steve_Laubach)\
**Post date:** [March 4, 2022, 7:52pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-addressing/56861/3 "2022-03-04T19:52:26Z")

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For reference  
[https://docs.inductiveautomation.com/display/DOC80/Modbus+Addressing](https://docs.inductiveautomation.com/display/DOC80/Modbus+Addressing)

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<div class="post-metadata">

**Author:** ![Jatin\_Kumar\_Singh](https://avatars.discourse-cdn.com/v4/letter/j/87869e/32.png) [@Jatin\_Kumar\_Singh](https://forum.inductiveautomation.com/u/Jatin_Kumar_Singh)\
**Post date:** [March 7, 2022, 3:27pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-addressing/56861/4 "2022-03-07T15:27:47Z")

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Hi Phil,

I tried using both the options, it still returns a 0 although the line is running. I also tried reverse word order, but no change to the value of the tag.

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<div class="post-metadata">

**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [March 7, 2022, 3:31pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-addressing/56861/5 "2022-03-07T15:31:19Z")

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Try reading those and nearby registers as 16-bit integers to see what the underlying activity is. That would be:

```auto
[Elrest]1.HR240
[Elrest]1.HR241
[Elrest]1.HR242
[Elrest]1.HR243

```

{Make temporary integer tags for those to show us the values.}

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<div class="post-metadata">

**Author:** ![Jatin\_Kumar\_Singh](https://avatars.discourse-cdn.com/v4/letter/j/87869e/32.png) [@Jatin\_Kumar\_Singh](https://forum.inductiveautomation.com/u/Jatin_Kumar_Singh)\
**Post date:** [March 7, 2022, 3:35pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-addressing/56861/6 "2022-03-07T15:35:36Z")

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![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/4/9/49a0d935570ba23a84098f3be4952f59622d2d04.png)

Still 0. The quality of the tag is good.

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<div class="post-metadata">

**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [March 7, 2022, 3:37pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-addressing/56861/7 "2022-03-07T15:37:49Z")

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There aren’t many other possibilities:

- The manual you have is wrong.
- There’s some configuration required for that rate to be reported as documented.
- The slave address (node) is wrong.
- The IP address is pointing at something else that happens to have zeroes there.

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<div class="post-metadata">

**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:** [March 7, 2022, 3:40pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-addressing/56861/8 "2022-03-07T15:40:13Z")

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At this point I would take Ignition out of the loop, try ModPoll etc and see what it is reporting…

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<div class="post-metadata">

**Author:** ![Jatin\_Kumar\_Singh](https://avatars.discourse-cdn.com/v4/letter/j/87869e/32.png) [@Jatin\_Kumar\_Singh](https://forum.inductiveautomation.com/u/Jatin_Kumar_Singh)\
**Post date:** [March 7, 2022, 10:03pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-addressing/56861/9 "2022-03-07T22:03:11Z")

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![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/e/7/e779b9669f427ed07b5c5dd6a1336c0a39b15cd4.jpeg)

I think they have given the wrong registers. Even ModPoll says 0 for these registers.