Today, more and more industries are considering moving towards being Industry 4.0 compliant. But this transition is not straightforward due to many reasons: in particular, transfer to new system can lead to significant production downtime and could result in delays and cost overruns. The best way is systematic seamless transition to newer and advanced technologies that Industry 4.0 offers. This paper proposes an automated synthesis framework that learns the behavior of existing legacy and often black-box programmable logic controllers and generates state machines that can be incorporated into IEC 61499 function blocks. The paper presents the toolchain architecture and exemplifies it on a laboratory scale Festo didactic mechatronic system.