Device and method for interface effective/ineffective state judging by varying threshold voltage to an input receiver circuit

An interface effective/ineffective state judging device for judging whether a predetermined interface is in an effective state where data communication via said interface can be effectively established or in an ineffective state where data communication via said interface cannot be effectively established, comprising:

• first level judging means for judging whether an input signal externally inputted to said predetermined interface is higher or lower than a first threshold value which is a value within an amplitude range of said input signal and is higher than said input signal in a case where the interface is in said ineffective state;
• second level judging means for judging whether the input signal is higher or lower than a second threshold value which is a value within the amplitude range of said input signal and is lower than said input signal in a case where the interface is in said ineffective state;
• means for judging that said interface is in the ineffective state when it is judged that said input signal is lower than said first threshold value and it is judged that said input signal is higher than said second threshold value;
• means for judging that said interface is in the effective state when it is judged that said input signal is higher than both said first threshold value and said second threshold value;
• and
• means for judging that said interface is in the effective state when it is judged that said input signal is lower than both said first threshold value and said second threshold value.

An interface effective/ineffective state judging method in which it is judged whether or not a predetermined interface is in an effective state where data communication via said interface can be effectively established or in an ineffective state where data communication via said interface cannot be effectively established, comprising the steps of:

• judging whether an input signal externally inputted to said predetermined interface is higher or lower than a first threshold value which is a value within an amplitude range of said input signal and is higher than said input signal in a case where the interface is in said ineffective state;
• judging whether the input signal is higher or lower than a second threshold value which is a value within the amplitude range of said input signal and is lower than said input signal in a case where the interface is in said ineffective state;
• judging that said interface is in the ineffective state when it is judged that said input signal is lower than said first threshold value and it is judged that said input signal is higher than said second threshold value;
• judging that said interface is in the effective state when it is judged that said input signal is higher than both said first threshold value and said second threshold value;
• and
• judging that said interface is in the effective state when it is judged that said input signal is lower than both said first threshold value and said second threshold value.