| 摘要 |
PURPOSE:To select a device card securely by inhibiting response signals, outputted from two devices simultaneously, from entering a computer and by informing the computer of this abnormality. CONSTITUTION:Device cards 2a-2n are each equipped with an address coincidence detecting circuit 5 which detects coincidence between a device address (DA) stored in its DA register 4 and that sent from a computer 1 via an output line 3 and then outputs a response signal. Further, each card has a response signal generating circuit 6 which outputs an answer signal inputted one of the circuits 5, but inhibits the outputting of response signals inputted simultaneously from two out of those circuts 5, and a multiple response detecting circuit 7 which detects response signals outputted simultaneously two out of the circuits 5 and informs the computer 1 of the abnormality via a common line 8. The circuits 6 are chained and when two response signals of the circuits 6 have logic 1s at the same time, their outputs have logic 0s and an L-level signal is sent to the signal line 8, so that the computer 1 knows the occurrence of the abnormality. |
