Hello friends,  I'm in the same situation. 
I need to read g code codes on the s7 1200.
 Has anyone managed to do it from scratch? 
Or would there be a Siemens block ready? 
Could you give me some light?

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Split from 3 axis drilling machine using S7-1200 PLC.

There is nothing ready-built for S7-1200 and once you start looking into its capabilities, you will see why Siemens didn't try (yet).

Having said that, I think you might be able to get something going.

Firstly, this will be a big effort.  So if it's a one-off machine, I think you're better off swapping it out for a T-CPU and using this:

https://support.industry.siemens.com/cs/document/109767009/

If you are going to automate many similar machines and you want to cut costs, maybe S7-1200 might be viable.  BUT please keep in mind that its ability to create curved paths is very limited - this is NO platform for CAD-CAM!!

The following library is for S7-1500T Kinematics, but you might be able to get some ideas & a head-start looking at the g-code blocks, if they are not locked.  I haven't checked:

https://support.industry.siemens.com/cs/document/109755891/

In order to achieve curved paths, you'll need to spam motion commands:

•  A dodgy way to do this is continually update a motion command by toggling the Execute input so that it is updated with your new speed/position commands.  The accuracy/resolution is limited in this case.  Also pay attention to acceleration / deceleration / jerk values because they are fixed.
• I haven't tried this, but you may be able to achieve a curved path using a S7-1200 motion command table technology object.  It has only 32 entries, and I don't know it's capabilities in terms of on-the-fly updates or chaining two motion tables together.  Also, I am not sure what accuracy / resolution you can achieve.

Hope that helps