| 摘要 |
PURPOSE:To avoid the data errors due to the invalid transfer data by detecting the foul activation of the mask information for a bus controller where the mask information showing the validity of data is transferred in addition to the data transferred via plural stages. CONSTITUTION:A decoder 1001 serves as a 1st detecting means which detects the discontinuous active state of the mask information based on the combination of active and inactive states of the mask bits in one stage. The flag means 1002-1009 and 1011 detect that the active state is changed to the inactive state within a stage and between stages for the mask bit of the mask information having the continuous active state and set the flags in active states. Then an OR gate 1002 and an AND gate 1010 which serve as the 2nd detecting means detect that the mask bit is changed again to the active state within the same bus cycle when the flags are kept under active states. Thus it is possible to avoid the transformation of the data and other faults owing to addition of such means that can detect a foul state of the mask information. |
