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Logic Gates - Technical MCQs

Q1:

A logic probe is again applied to the pins of a 7421 IC with the following results. Is there a problem with the circuit and if so, what is the problem?

A Pin 6 should be ON.

B Pin 8 should be ON.

C Pin 8 should be pulsing.

D no problem

ANS:D - no problem

Ic 7451 is a 14 pin IC, pin 7 is GND & pin 14 is Vcc. So here vcc is applied then ic is in on state & now the 2 and gates have 1, 2, 4, 5 as inputs &6 as output pin & another gate has 13, 12, 10, 9 as inputs and 8 as output.

Here given that;

1-on, 2-changing, 4, 5 -on, so output pin 6 depends on only input 2.

10th pin is in the off state so we can get 8 pin always off, by this we can say that there is no need to change the conditions all are correct.