Importance

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Abstract

A duplexing system and method for writing a back-up list in which a back-up process is substituted for a process having an error while performing plural processes. Memory space to store a back-up order list is allotted to two bytes per process. A number of the leading order process is stored in the first byte, whereas a number of following order process is stored in the second byte. Further, the top priority bit or the last bit of each byte of memory space in which the process to be backed-up is allotted is set, and thus the existence of a registration is displayed. Further, if error an occurs at plural processes, a non back-up process generates a back-up order list according to time sequence of error generation. If an error occurs at a process of another top priority order while operating a back-up of a back-up process, the process is registered at the leading order list. If a process in a back-up procedure is restored at the present back-up process, the back-up process is in a waiting status, and the top priority order process is detected from a back-up list memory and is backed-up. If any one process among processes registered in the present back-up list memory is restored, a corresponding item is deleted from a back-up list memory. The leading item is connected to the following item, and thus an order retrieval of a back-up list is conveniently performed.

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First Claim