Abstract: A flowchart-based programming and control system includes a computer with a processor, memory, and a display. A device is associated with a process. A flowcharting module executed by the computer generates and edits flowchart source code that contains action and decision blocks which define logic for operating the device to further the process. An external function can be called from one of the action and decision blocks during run time. The external function is executed by an external function module which receives input parameters and generates return values. The external function is preferably a dynamic link library (DLL). Since the external functions are loaded during run time only when they are needed, they do not consume system memory until they are used.