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I am new in PLCs, and I would like to can send data from the PLC to a PC application that it would be listening and the it could act in consecuence.

For example, the PLC detects an alarm and the it would send this alarm to the PC. The PC receive this message and then does something like send an email, save the data in a database or another things.

I have read the documentation about libraries like Sharp7, S7Net, S7Net Plus and others, but the examples that I see is that the PC reads data from the PLC, but it doesn't receive data from the PLC.

I see an example in which the PC is reading in while / true loop the variables in the PLC, but I guess it is a worse solution buecause it requieres more resources, I think it is better if the PLC could notify the alarm and then PC is just waiting if something happend and handle it when it is notify.

Thanks.

Álvaro García
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    check this:http://www.plctalk.net/qanda/showthread.php?t=96372 and this:https://github.com/search?l=C%23&q=PLC-PC&type=Repositories – Zakaria Najim Nov 27 '22 at 21:03
  • @ZakariaNajim Thanks for the links. In the forum that you give me it talks about send data from PLC to PC, I would like the contrary process, that the PLC sends data to PC to notify events. But the resources that you give me it is a good way to follow. – Álvaro García Nov 28 '22 at 09:07
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    @Álvaro I recommend looking into [MQTT](https://cache.industry.siemens.com/dl/files/872/109748872/att_1006438/v4/109748872_MQTT_Client_DOKU_V2-1_en.pdf). You would be able to send messages on demand (when an alarm occurs), and this would trigger an event in your program to act upon receiving the message. – dwpessoa Nov 28 '22 at 10:59

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There are a number of ways to do this.

You can use OPC/UA and subscribe to PLC data. You will need to purchase an OPC/UA license to install on the PLC. Here is a guide, with an example Visual Studio project, which has a subscription feature: Creating of OPC UA clients with .NET and helper class

You can use MQTT as mentioned by dwpessoa. Here's a link to the SIOS page related to the link he posted, including a sample TIA Portal project: Use the SIMATIC controller as an MQTT client

You could use TCP sockets. The PLC transmits strings of data to the PC. You can set an event for incoming data in your code. Search for help on the TCON / TSEND instructions, or for a rather thorough example, see here: Basic Examples for Open User Communication (OUC)

You can even write to a MS SQL database on the PC if you like: Connecting a S7-1200 PLC / S7-1500 PLC to a SQL Database

And there are more...

Cliff Pennalligen
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