DETECTING SYSTEM FOR UNMOUNTED PRINTED BOARD

PURPOSE:To attain the detection of the unmounting of an option printer board usefully by providing a means which detects the presence/absence of the printed board to be mounted selectively, and a means which informs the unmounting of the printed board to a processor when the processor accesses to the printed board. CONSTITUTION:When an option printer board P2 is unmounted, a detection signal S7 is pulled up, and its logic level goes to H. A wait time control circuit 4 makes ready instantly a ready signal S6 using the detection signal S7 of H level, and a chip select signal S3, and a processor progresses its operation without delay, but, at such a time, an interruption signal S8 is generated since both inputs at an AND circuit 7 are at H levels. By defining uniquely that the generating factor of the interruption signal means the unmounting of the option printer board P2, the unmounting of the option printer board P2, and the invalidness of an access to its area can be informed to a processor 1 with the generation of a request signal. In this way, the processor 1 can detect the unmounting of the printed board without spending a wasteful time.