# Clarification on Modbus RTU over TCP

**URL:** <https://forum.inductiveautomation.com/t/clarification-on-modbus-rtu-over-tcp/78191>\
**Category:** General Discussion\
**Tags:** ignition81\
**Created:** [August 22, 2023, 5:07am UTC](https://forum.inductiveautomation.com/t/clarification-on-modbus-rtu-over-tcp/78191 "2023-08-22T05:07:35Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Henrol\_Jeo\_Gutierrez](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/henrol_jeo_gutierrez/32/50993_2.png) [@Henrol\_Jeo\_Gutierrez](https://forum.inductiveautomation.com/u/Henrol_Jeo_Gutierrez)\
**Post date:** [August 22, 2023, 5:07am UTC](https://forum.inductiveautomation.com/t/clarification-on-modbus-rtu-over-tcp/78191/1 "2023-08-22T05:07:35Z")

</div>

Hi I have a modbus devices connected in serial, and a gateway that converts the serial into ethernet (modbus TCP).

Below is the simplest diagram on what is my setup:

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/b/5/b5b7f48930739d6fbd2670eeaef6fff8b13fa82a.png)

I am new to Ignition gateway, but my simple question is how am I going to read data for each of my devices, (the number of below each devices are their slave IDs).  
I found these modbus RTU over TCP driver in Ignition, but I am not sure if I am configuring it right, supposed if I wanna read data on slaveID 5, should I put something like this on the local address option?

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/5/7/57621a7c455b7f94770a18529bacd40df8ecef6c.png)

And I need to add more devices (RTU over TCP) for each slave IDs I have?  
To be honest I am also not sure if I am using the right device (the RTU over TCP) or should I use the modbus TCP device for this setup?

Thanks and regards,  
Henjoe

---

<div class="post-metadata">

**Author:** ![Martial\_Wilbert](https://avatars.discourse-cdn.com/v4/letter/m/3ab097/32.png) [@Martial\_Wilbert](https://forum.inductiveautomation.com/u/Martial_Wilbert)\
**Post date:** [August 22, 2023, 10:34am UTC](https://forum.inductiveautomation.com/t/clarification-on-modbus-rtu-over-tcp/78191/2 "2023-08-22T10:34:04Z")

</div>

Hi Henjoe,  
On the tag OPC path, you can specify the slave ID: [DeviceName]SlvID.PointAd

e.g. : [TEST]1.C123 for the Coiler on slave 1  
Then you can use [TEST]2.C123

Information on this page: [Modbus Addressing - Ignition User Manual 8.0 - Ignition Documentation (inductiveautomation.com)](https://docs.inductiveautomation.com/display/DOC80/Modbus+Addressing)  
Search for Unit ID

Hope it helps.

Martial

---

<div class="post-metadata">

**Author:** ![Henrol\_Jeo\_Gutierrez](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/henrol_jeo_gutierrez/32/50993_2.png) [@Henrol\_Jeo\_Gutierrez](https://forum.inductiveautomation.com/u/Henrol_Jeo_Gutierrez)\
**Post date:** [August 22, 2023, 11:50am UTC](https://forum.inductiveautomation.com/t/clarification-on-modbus-rtu-over-tcp/78191/3 "2023-08-22T11:50:03Z")

</div>

Thanks @Martial_Wilbert for this info!

Highly appreciated.

Regards