| 摘要 |
PURPOSE:To back up plural control programs and at the same time to avoid a malfunction with a central processing unit which has just a function to back up a single program, by adding a follower control program display memory, etc. CONSTITUTION:When the control is shifted from the schedule of a main control program OS 1 to that of a follower OS 2a1, the OS 2a1 executes its own schedule and produces a TRAP instruction to the OS 1 to change the state display flag of the OS 2a1 immediately before the control is shifted to a controlling follower task 31. The OS 1 knows the generation of the TRAP instruction through a follower OS state display memory 6 and executes the schedule after the processing is over with the TRAP instruction (showing the change of the state of the OS 2a1). In addition, a memory protecting circuit 6a which can change the OS state display flag only in a supervisor mode is provided to facilitate easy back-up of the TRAP instruction within a follower task. At the same time, the system malfunctions are avoided. |
