# Modbus TCP driver

**URL:** <https://forum.inductiveautomation.com/t/modbus-tcp-driver/10542>\
**Category:** General Discussion\
**Created:** [September 29, 2015, 11:19am UTC](https://forum.inductiveautomation.com/t/modbus-tcp-driver/10542 "2015-09-29T11:19:48Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![joaopmrod2](https://avatars.discourse-cdn.com/v4/letter/j/90ced4/32.png) [@joaopmrod2](https://forum.inductiveautomation.com/u/joaopmrod2)\
**Post date:** [September 29, 2015, 11:19am UTC](https://forum.inductiveautomation.com/t/modbus-tcp-driver/10542/1 "2015-09-29T11:19:48Z")

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I’ve been trying to use the Modbus TCP driver to communicate with a custom made Modbus device that implements the python modbus-tk module. I am able to communicate (both read and write registers) with is using any modbus master test software. However, when I try to do it from Ignition I’m able to write to the device’s registers but I can’t read them. I always get this message on the quick client:

Read completed. [Ignition OPC-UA Server]ns=1;s=[aaaaaa]1.a0  
Status: Bad  
Value: null  
Quality: [Bad] Bad; unspecified.  
Timestamp: 01-01-1601 0:00:00 GMT

I’ve also tried to run a test Modbus server ([modbusdriver.com/diagslave.html](http://www.modbusdriver.com/diagslave.html)). Although it works perfectly with my modbus test client software it happens exactly the same in Ignition, I can write to the server but I can’t read from it. I always get the same error.

I’ve already tried different advanced configurations on the device page on Ignition.

Any idea on how can I solve this problem?

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**Author:** ![AlThePal](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/althepal/32/3603_2.png) [@AlThePal](https://forum.inductiveautomation.com/u/AlThePal)\
**Post date:** [September 29, 2015, 12:39pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-driver/10542/2 "2015-09-29T12:39:11Z")

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It’s at this stage I usually reach for Wireshark to have a look at the actual data being sent and received. If you can do this and post the comms traffic it will be easier to diagnose.

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**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\
**Post date:** [September 29, 2015, 2:19pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-driver/10542/3 "2015-09-29T14:19:29Z")

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+1 for Wireshark.

It would also be useful to know what you’ve mapped a0 to. Usually it’s easier to troubleshoot without the mappings set up - just create a tag in the designer that addresses [aaaaaa]1.HR1 for example.

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<div class="post-metadata">

**Author:** ![joaopmrod2](https://avatars.discourse-cdn.com/v4/letter/j/90ced4/32.png) [@joaopmrod2](https://forum.inductiveautomation.com/u/joaopmrod2)\
**Post date:** [September 29, 2015, 8:36pm UTC](https://forum.inductiveautomation.com/t/modbus-tcp-driver/10542/4 "2015-09-29T20:36:41Z")

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I formated my laptop and re-instaled windows and ignition… It solved the problem.