PURPOSE:To locate a faulty processor on the occurrence of a fault in the operation of the decision of a bus operating processor by testing a bus operating request function in a single processor and a bus master controller of all processors connecting to the bus. CONSTITUTION:Gates 7,8 are 'through' when a bus master controller 1 is in operation in the on-line operation and a polling signal in the on-line operation and a bus operating request signal in the on-line operation are sent/received to/from a bus 9. When a diagnostic controller 3 is set to the diagnostic mode by a command from the firmware, the controller 3 activates the bus master controller 1, gives a command to close the gates 7,8 to the gate controller 4 to stop the gates 7,8. Moreover, the diagnostic controller 3 gives a command to selectors 5,6 to activate a polling signal in the diagnostic mode and a bus operating request signal in the diagnostic mode. Thus, the bus selection in the inside of the processor is attained.
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