Personal computer interrupt line sharing circuit with active interrupt line monitoring, and method for sharing a common interrupt line by active monitoring

Abstract

In an interrupt line sharing circuit for a personal computer system, which has a plurality of instruments and one common interrupt line provided in common to the plurality of instruments, a personal computer executes a predetermined I/O access at each time the personal computer has completed an interrupt processing. Each of the plurality of instruments comprises an I/O monitoring circuit for monitoring whether or not the predetermined I/O access has been performed, and an interrupt line monitoring circuit monitoring the common interrupt line, for judging that an interrupt processing has been started if an interrupt request has been sent onto the common interrupt line from one of the instruments. The interrupt line monitoring circuit also judges that the interrupt processing has been completed when the I/O monitoring circuit detects the predetermined I/O access. An interrupt line control circuit discriminates a busy/not-busy condition of the common interrupt line on the basis of the start and the completion of the interrupt processing judged by the interrupt line monitoring circuit. The condition of the common interrupt line ensures that the interrupt request generated in the plurality of instruments is sent the interrupt line after the completion of the interrupt processing.