Driver Lockout Circuit
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-05
The arrangement provides a test for a circuit which normally functions only when the microprocessor is reset, yet requires the microprocessor to be active to fully exercise it. Use is made of an operational amplifier (op-amp) circuit with slightly less than unity gain to force one input of a comparator to be just slightly lower than the reference voltage on the other input of the comparator. Also, extra current is forced through a voltage reference on a card-under-test (CUT) so that the voltage reference will always be higher than the threshhold voltage for deactivating the reset image to the microprocessor. A combination of these techniques is used to run a test on driver outputs (via microcode) while the lockout is activated. Fig.