What does the CALL instruction allow?

• A. The CALL instruction duplicates the program to a new memory address.
• B. The CALL instruction creates a loop within the same job without subroutine.
• C. The CALL instruction sends a diagnostic signal to PLC.
• D. The CALL instruction allows one job to open another as a subroutine. The parent is caller, child is called; optional RET or END; controller resumes execution of the parent after the CALL.

Answer: (D)

The CALL instruction lets a program transfer control to another program segment, treating that segment as a subroutine that can be executed and then return control to the calling program. The parent is the caller and the child is the called subroutine; the flow is designed so, after the subroutine finishes (typically via a return, or the subroutine ending), execution resumes in the original program where the CALL occurred. This enables modular, reusable code—putting common sequences in a subroutine and invoking them from multiple places without duplicating logic. The other descriptions don’t match how subroutine calls work: they don’t duplicate programs, create loops within the same job without subroutines, or send diagnostic signals.