What role do highlighted instructions serve within a PLC program?

Highlighted instructions within a PLC (Programmable Logic Controller) program serve as a method of program interlocking. This means they are used to ensure that certain conditions must be met before allowing further actions or outputs to occur within the system. By employing highlighted instructions for interlocking, programmers can design safety measures and logical sequences that prevent system malfunctions or unsafe operations.

For example, a highlighted instruction might check whether a safety guard is in place before allowing a machine to operate. This helps to establish a safe operational environment and ensures that all necessary preconditions are satisfied to maintain system integrity and performance. Thus, interlocking through highlighted instructions is crucial for enhancing reliability and safety in PLC programming.