The growing need for smart and flexible systems in many areas of industry, such as manufacturing, smart grids, building automation systems and others, has resulted in new design approaches such as Cyber-physical systems (CPS). This raised the need for formal modelling of these systems to address reliability and robustness requirements. This paper addresses the problem of developing a formal semantics, based on abstract state machines (ASM), for modelling of distributed control systems for industrial CPS based on the IEC 61499 standard. The developed approach allows to build formal models of flexible distributed control systems for analysis and verification of various properties.