# Siemens acting as a Modbus server to Ignition

**URL:** <https://forum.inductiveautomation.com/t/siemens-acting-as-a-modbus-server-to-ignition/66252>\
**Category:** Ignition\
**Created:** [November 8, 2022, 7:36pm UTC](https://forum.inductiveautomation.com/t/siemens-acting-as-a-modbus-server-to-ignition/66252 "2022-11-08T19:36:36Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Ahutomation](https://avatars.discourse-cdn.com/v4/letter/a/eb9ed0/32.png) [@Ahutomation](https://forum.inductiveautomation.com/u/Ahutomation)\
**Post date:** [November 8, 2022, 7:36pm UTC](https://forum.inductiveautomation.com/t/siemens-acting-as-a-modbus-server-to-ignition/66252/1 "2022-11-08T19:36:36Z")

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I was reading through the posts and noticed that the OPC UA with the Siemens 1500 tends to put some overhead in the plc, besides the s7 driver that ignition includes, and the OPC UA , can the communication be through Modbus TCP ? the PLC talking Modbus to ignition?... can the OPC UA overhead be solved by creating different OPC UA servers (different PLCs) ? How many Datablocks are OK for the PLC to handle in OPC UA ?

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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:** [November 8, 2022, 7:53pm UTC](https://forum.inductiveautomation.com/t/siemens-acting-as-a-modbus-server-to-ignition/66252/2 "2022-11-08T19:53:11Z")

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> [@Ahutomation](#):
>
> the PLC talking Modbus to ignition?

Yes, with this module:

> **[Ignition Third-Party Module Showcase](https://inductiveautomation.com/moduleshowcase/module/automation-professionals-llc-advanced-modbus)**
>
> Easily extend Ignition's core functionality with Third-Party Modules. The Module Showcase is a great place to find a solution that best meets your needs.

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<div class="post-metadata">

**Author:** ![Ahutomation](https://avatars.discourse-cdn.com/v4/letter/a/eb9ed0/32.png) [@Ahutomation](https://forum.inductiveautomation.com/u/Ahutomation)\
**Post date:** [November 8, 2022, 8:30pm UTC](https://forum.inductiveautomation.com/t/siemens-acting-as-a-modbus-server-to-ignition/66252/3 "2022-11-08T20:30:03Z")

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If the 1500 plc can become a server itself, why would it need a middle man ?, shouldn't it be connected through ethernet ?

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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:** [November 8, 2022, 10:13pm UTC](https://forum.inductiveautomation.com/t/siemens-acting-as-a-modbus-server-to-ignition/66252/4 "2022-11-08T22:13:18Z")

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You asked about the PLC talking **TO** Ignition. If you use the PLC's OPC server, then the PLC is being talked to **FROM** Ignition.

There are limits and limitations in the Siemens on-board OPC that annoy some users. Having another path, in the other direction, may be useful.

(The linked module is a Modbus implementation that supports RS-232, RS-485, raw serial over ethernet, and Modbus TCP--also ethernet.)