TO: Pierogoal:
lad和stl is two of program language. We you start program, you can select which language you want. Normally, LAD can be transfered to STL at any time, but STL cann't.

These two language are similar, and both are low level machine language.

Include LAD,STL, there are FBD,SCL,CFC,SFC program laguage for Simatic PLC.