| 摘要 |
PURPOSE:To prevent a low-speed device from failing a access by switching plural coupled circuits and counting the coupling frequency of every coupled circuit coupling with a host device, and inhibiting only a specific host device from being coupled. CONSTITUTION:Selection detection rejecting circuits 10 and 11 detect signals of ports A and B. If the circuit 10 selects a selction signal, an FF14 is set through an AND gate 12 and an AND gate 15 outputs 1 to set an FF19 through an OR gate 18. An AND gate 20 also outputs 1 and the circuit 11 rejects the signal of the port B. A coupling counter 22 counts the coupling frequency of the port A to makes a comparison 23 with a predetermined threshold value 24, and outputs 1 when the counted value exceeds the threshold value to set an FF27 through an AND circuit 28. Then, the selection detection rejecting circuit 10 is set through an OR circuit 16 to reject the signal from the port A. The selection detection rejecting circuit 11 is enabled to accpet the signal from the port B. Consequently, only specific device is inhibited from being coupled. |
