PRIORITY PROCESSING SYSTEM OF INFORMATION TRANSFER CONTROL

PURPOSE:To eliminate the need to giving priority levels to all of input/output devices, and reduce the amount of circuit by setting only the number corresponding to a specific input/output device among plural input/output devices in a priority register. CONSTITUTION:A clock is normally supplied to the priority register 29, whose contents are updated. If a request for registering the number of the specific input device in a stack is made while the stack is full, the stack request is permitted only when a registration request having the number set in the priority register 29 or a higher priority number is made; and the permission of stack registration requests from other input/output devices are inhibited.