Communication with Siemens S7-300 PLC

[razm]

Hello

I want to write my own HMI program that will communicate with a Siemens S7-300 via the Ethernet port.
I know how to open a port in the PC that will send data over TCP. What I need to know is:
1. What do I need to do in the PLC
2. How the message should be written

 

[JesperMP]

Most HMIs polls the data that is to be displayed, and sends eventual changed values (i.e. setpoints). So there is normally no need to do anything in the PLC program.

It is also possible to have the PLC send the data rather than the HMI polling the data, but that is not typical.

Are you using some kind of communication library to let your selfmade HMI program communicate with the S7 PLC ?

 

[adfox]

I've done several logging apps using this:

http://snap7.sourceforge.net/

There's also Moka7 for Java.