| 摘要 |
PURPOSE:To suppress an influence of trouble to facilitate clearing-up of the cause of trouble by providing a common bus use permitting device which has a function to mask the bus use request of an input/output device where trouble occurs. CONSTITUTION:A mask setting circuit 1 receives a mask request signal (q) and outputs a mask signal (i) to a mask circuit 2. The mask circuit 2 receives a bus use signal (a) from each input/output device. The mask circuit 2 operates AND between signals (a) and (i) to output a signal (b). A request accepting circuit 31 outputs the signal (b) as a synchronizing signal (c) synchronously with a clock (j). Priority levels of input/output devices are stored in an arbitration information storage circuit 32, and the circuit 32 discriminates the input/ output device having the highest priority level in the synchronizing signal (c) and outputs data (d) indicating that this input/output device requests the bus use. A bus use permission signal output circuit 35 outputs a bus use permission signal (f) to the specified input/output device. |
