# Modbus RTU over TCP timeout

**URL:** <https://forum.inductiveautomation.com/t/modbus-rtu-over-tcp-timeout/63717>\
**Category:** Ignition\
**Created:** [September 2, 2022, 3:02pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-over-tcp-timeout/63717 "2022-09-02T15:02:25Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Callmesoon](https://avatars.discourse-cdn.com/v4/letter/c/c67d28/32.png) [@Callmesoon](https://forum.inductiveautomation.com/u/Callmesoon)\
**Post date:** [September 2, 2022, 3:02pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-over-tcp-timeout/63717/1 "2022-09-02T15:02:25Z")

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Hi guys, i am able to use modscan to read the devices with stable connection when i use ignition to read, the tag quality will become bad and after some time, it will be back to good again. I have tried to increase the scan time of the tag to 10000 ms but is still the same. I also tried to reduce the number of read holding register per request since i am only reading holding register but the result is still the same. Not sure what i have went wrong in the set up

I am current using ignition 8.1.15.  
I found these in the log.

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/e/d/ed5f16a1aafb3359dc4addd58a8f5f4c60a245ed.jpeg)

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**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:** [September 2, 2022, 3:16pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-over-tcp-timeout/63717/2 "2022-09-02T15:16:56Z")

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Using an ethernet-to-serial interface for Modbus RTU requires careful setup of the buffering options on that interface. The advice I give in my [Advanced Modbus Module](https://inductiveautomation.com/moduleshowcase/module/automation-professionals-llc-advanced-modbus)’s Moxa application notes (in the [manual](https://www.automation-pros.com/modbus/UserManual.pdf)) would apply to IA’s native driver, and similar settings would be needed for other branded interfaces.

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**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:** [September 2, 2022, 3:21pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-over-tcp-timeout/63717/3 "2022-09-02T15:21:44Z")

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Also, in case it isn’t obvious, only one system can talk to that interface. Modbus RTU, whether over TCP or not, is single-master. If you need multiple simultaneous masters, you will need an actual Modbus TCP to Modbus RTU _ **gateway** _.

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**Author:** ![jay](https://avatars.discourse-cdn.com/v4/letter/j/ed8c4c/32.png) [@jay](https://forum.inductiveautomation.com/u/jay)\
**Post date:** [September 2, 2022, 7:33pm UTC](https://forum.inductiveautomation.com/t/modbus-rtu-over-tcp-timeout/63717/4 "2022-09-02T19:33:01Z")

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Modscan reads unit id 1 by default. Unless you specify unit id 1 in Ignition ( [device]1.HRxxxx ) you will be reading unit id 0. Your Modbus server/slave may not respond to unit id 0.