| 摘要 |
PURPOSE:To detect a disturbance quickly, when it has been generated in an input/output bus by sending out a test data to the input/output bus in a closed period of a bus gate circuit, and comparing and deciding whether the test data has been generated correctly in the input/output bus or not. CONSTITUTION:A CPU 10 designates an output unit 16, sends out an output data to a data bus DBn by opening an output of a bus gate circuit 22, and also sets a control signal IOEN to an L level once, and thereafter, returns it to an H level. As a result, an output data on an input/output bus IODn is latched to a unit 16. In a monitoring circuit 24, a multiplexer 30 is switched to the bus DBn side, and a buffer circuit 28 is closed. Accordingly, when the CPU 10 has outputted the data by opening the circuit 22, the data on the bus DBn and the data on the bus IODn are compared by a coincidence circuit 32. If there is no disturbance in the bus IODn, both the data coincide with each other naturally, and if a disturbance occurs, both the data do not coincide. A dissidence output in this comparing operation is read to a flag circuit 34. |
