In this work we will present a method for automatic test case generation for PLC-software. We support the coverage criteria line coverage and branch coverage. The test cases are generated using a model-checker, which iteratively creates program traces, each of them covering a part of the coverage criteria. The process results in a set of test cases that in sum cover all lines or branches in the program. Test cases are generated in Structured Text, allowing the execution on a soft-PLC or the actual hardware. Results on industrially used function blocks show the scalability of our approach.