Testing for time-related behaviors of PLC software is important and should be performed carefully. We propose a structural testing technique on Function Block Diagram(FBD) networks including timer function blocks. In order to test FBD networks including timer function blocks, we generate templates for timer function blocks and transform a unit FBD into a flowgraph using the proposed templates. We apply existing testing techniques to the generated flowgraph and describe how the characteristics of timer function blocks are reflected in the testing process. By the proposed method, FBD networks including timer function blocks can be tested thoroughly without the intermediate code which was essential in the previous FBD testing. To demonstrate the effectiveness of the proposed method, we use a trip logic of bistable processor of digital plant protection systems which is being developed in Korea.

Automated static timing analysis methods provide a safe but usually overestimated worst-case execution time (WCET). Overestimation is mainly due to the existence of the execution paths that turn out to be infeasible or unrealistic when dynamic behavior of the program or environmental assumptions are fully considered. In this paper, we propose a new method and a visual language called User Constraint Language (UCL) to obtain a tight WCET estimation. In our method, both the program and flow information are represented by single formalismfinite automata. UCL provides intuitive visual notations with which users can easily specify various levels of flow information to characterize the execution paths of program. The user constraints specified in UCL are translated into finite automata. The combined automaton constructed by a cross-production of the automata for program and user constraints reflects the static structure and possible dynamic behavior of the program. It contains only the execution paths satisfying user constraints from which we can obtain a tight WCET using a path-based or Implicit Path Enumeration Technique (IPET)-based calculation method. A case study using part of a satellite flight software program demonstrates the effectiveness of UCL and our approach. 12

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