# Modbus Communication with SEL RTAC **URL:** \ **Category:** Ignition\ **Created:** [August 25, 2023, 1:35am UTC](https://forum.inductiveautomation.com/t/modbus-communication-with-sel-rtac/78364 "2023-08-25T01:35:28Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![rsnaik](https://avatars.discourse-cdn.com/v4/letter/r/c0e974/32.png) [@rsnaik](https://forum.inductiveautomation.com/u/rsnaik)\ **Post date:** [August 25, 2023, 1:35am UTC](https://forum.inductiveautomation.com/t/modbus-communication-with-sel-rtac/78364/1 "2023-08-25T01:35:28Z")
We have SEL RTAC 3555 we are trying to communicate over the Modbus protocol. Below is error we are facing. ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/0/4/041c1ae8b902173eec32990b9690e0a8b3b464ad.png) Appreciate your help to resolve this issue. We use Modsim32 and Modscan to test the modbus communication between RTAC and Ignition machine and its working good. Below are the packets capture using wire shark ##### Server sends TCP syn to RTAC ##### RTAC response with TCP syn ack acknowledging connection #### Server sends acknowledgement back to RTAC to complete the 3 way handshake. #### RTAC sends Fin to the Server to close the connection ---
**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:** [August 25, 2023, 2:05am UTC](https://forum.inductiveautomation.com/t/modbus-communication-with-sel-rtac/78364/2 "2023-08-25T02:05:46Z")
Have you created any OPC tags for this device yet? ---
**Author:** ![rsnaik](https://avatars.discourse-cdn.com/v4/letter/r/c0e974/32.png) [@rsnaik](https://forum.inductiveautomation.com/u/rsnaik)\ **Post date:** [August 25, 2023, 5:44pm UTC](https://forum.inductiveautomation.com/t/modbus-communication-with-sel-rtac/78364/3 "2023-08-25T17:44:20Z")
We are not able to browser the tag in OPC client. We discussed this with SEL they have raise a question "Is the Ignition system using TLS connection encryption? " ---
**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:** [August 25, 2023, 5:50pm UTC](https://forum.inductiveautomation.com/t/modbus-communication-with-sel-rtac/78364/4 "2023-08-25T17:50:00Z")
> [@rsnaik](#): > > We are not able to browser the tag in OPC client. Modbus protocol doesn't offer browsing. You need to manually create OPC tags with OPC Item Paths that use the address syntax described in the user manual: [Modbus Addressing - Ignition User Manual 8.1 - Ignition Documentation](https://docs.inductiveautomation.com/display/DOC81/Modbus+Addressing) > [@rsnaik](#): > > "Is the Ignition system using TLS connection encryption? " I don't see how this is relevant to Modbus. ---
**Author:** ![rsnaik](https://avatars.discourse-cdn.com/v4/letter/r/c0e974/32.png) [@rsnaik](https://forum.inductiveautomation.com/u/rsnaik)\ **Post date:** [August 25, 2023, 6:10pm UTC](https://forum.inductiveautomation.com/t/modbus-communication-with-sel-rtac/78364/5 "2023-08-25T18:10:33Z")
I tried creating OPC Tag, but no luck on that. The device status in device connections created to communicate with RTAC keep on switching from Connection to Connected and Disconnected, I would say it show connected for few sec. ---
**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:** [August 25, 2023, 6:12pm UTC](https://forum.inductiveautomation.com/t/modbus-communication-with-sel-rtac/78364/6 "2023-08-25T18:12:47Z")
> [@rsnaik](#): > > no luck on that. Please show what you tried. If you have no properly configured OPC tags, the channel is likely to time out (many, many devices time out after ten seconds). ---
**Author:** ![rsnaik](https://avatars.discourse-cdn.com/v4/letter/r/c0e974/32.png) [@rsnaik](https://forum.inductiveautomation.com/u/rsnaik)\ **Post date:** [August 25, 2023, 6:24pm UTC](https://forum.inductiveautomation.com/t/modbus-communication-with-sel-rtac/78364/7 "2023-08-25T18:24:21Z")
![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/f/6/f6a5354237e28b1e2b9fed00581d88799bb2d622.png) ---
**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:** [August 25, 2023, 6:29pm UTC](https://forum.inductiveautomation.com/t/modbus-communication-with-sel-rtac/78364/8 "2023-08-25T18:29:37Z")
> [@rsnaik](#): > > We use Modsim32 and Modscan to test the modbus communication between RTAC and Ignition machine and its working good. Try `[PSCADA]1.HR2` as the address instead. These other software often default to unit/slave ID 1 instead of 0, which is the default in Ignition. If you can also share some actual Wireshark captures of both the other software and of Ignition that would help as well. ---
**Author:** ![rsnaik](https://avatars.discourse-cdn.com/v4/letter/r/c0e974/32.png) [@rsnaik](https://forum.inductiveautomation.com/u/rsnaik)\ **Post date:** [August 25, 2023, 7:30pm UTC](https://forum.inductiveautomation.com/t/modbus-communication-with-sel-rtac/78364/9 "2023-08-25T19:30:09Z")
Thanks for sharing that @Kevin.Herron its work. Appreciate you support and help @Kevin.Herron and @pturmel Have a good day!