| 摘要 |
PURPOSE:To effectively use the output line of a central processing unit CPU and to surely inform the presence of an abnormal state, by outputting an abnormality informing signal to the output line of the CPU in a form different from the normal one when the abnormality is detected. CONSTITUTION:When an abnormal area or an abnormal state is detected, a part among the output signals B-D of output ports PO3-PO5 is set at L levels and the abnormality is informed to outside. For instance, the signal B is set at an L level in the case of the abnormality detected in the CPU itself, the signal C is set at an L level in the case of the abnormality detected in a ROM 2, and the signal D is set at an L level in the case of the abnormality detected in a RAM 3 respectively. Thus an external device can recognize the occurrence of the abnormality owing to a fact that the ports PO3-PO5 have unexpected level changes and also on which part the abnormality is generated only by checking the levels of the ports PO3-PO5. |
