WATCH DOG TIMER DEVICE FOR COMMUNICATION BUS

PURPOSE:To execute a time out processing irrespective of the amount of data, and to recognize a cause when generating the time out by providing hardware having a time out function to solve a difficult problem on a processing time in software and measuring the time for every one data transfer. CONSTITUTION:In a gate means 7, a communication operating state is detected by a hand shake signal and a time is counted in counters 11, 13 under the operating state. The counters 11, 13 generate a time out signal at the time of exceeding a time out value, apply an interruption to a central processing unit 18, control a gate 7 and prohibits an access to an internal circuit from an interface controller 5. When the counters 11, 13 are constituted of plural counters so as to time count the different communication operating states (can be detected by the gate means 7), the central processing unit recognizes from which counter a time out signal is outputted, and discriminates that what time out is generated.