Combining DC Stuck-Fault and AC Functional Tests
Original Publication Date: 1986-May-01
Included in the Prior Art Database: 2005-Mar-09
To test three-state circuits, a tester requires that load resistors pulled up to +2 volts be attached to these signals, as shown in Fig. 1. This allows the tester to establish a voltage that is above .8 volt and below 2.5 volts to test for the high-impedance state. Such loads are acceptable for address and data lines and do not affect the AC test. When the three-state circuits are active-low control signals, pull-up resistors ensure that the control signals float high and stay inactive when not driven. If the same tester loading used for normal three states is used for control three states (Fig. 2), the DC test will complete, but the AC test will fail. Because the control lines are held at 2.35 volts, the receiver gates on the logic card cannot always determine this voltage to be an up level.