If no ON-unit is in effect when a condition is raised a standard system action is taken (often this is to raise the codice_25 condition). The system action can be reestablished using the codice_186 option of the codice_180. With some conditions it is possible to complete executing an ON-unit and return to the point of interrupt (e.g., the codice_188 conditions) and resume normal execution. With other conditions such as codice_189, the codice_25 condition is raised when this is attempted. An ON-unit may be terminated with a codice_191 preventing a return to the point of interrupt, but permitting the program to continue execution elsewhere as determined by the programmer.