Testing circuit for a data interface

A testing circuit adapted for an interface, the testing circuit comprising:

• a first comparator, a negative input of the first comparator connected to the interface, a positive input of the first comparator being input a reference voltage;
• a second comparator, a positive input of the second comparator being input the reference voltage, a negative input of the second comparator connected to an output of the first comparator;
• a first display member connected to the output of the first comparator, the voltage of the interface being compared with the reference voltage, the first comparator outputting a signal to control the first display member to display a comparison result;
• a second display member connected to an output of the second comparator, the voltage from the output of the first comparator being compared with the reference voltage, the second comparator outputting a signal to control the second display member to display a comparison result;
• and
• a load feeding circuit, wherein the load feeding circuit comprises a resistance-regulating unit, a third comparator, a pass element, and a capacitor, a negative input of the third comparator is connected to the capacitor and a first terminal of the pass element, an output of the third comparator is connected to a second terminal of the pass element, a third terminal of the pass element is connected to the interface, a load applied to the interface is regulated by changing a resistance value of the resistance-regulating unit.