Digital Electronics-Logic Gates
Digital Electronics-Logic Gates
21. How many inputs of a four-input AND gate must be HIGH in order for the output of the logic gate to go HIGH?
- any one of the inputs
- any two of the inputs
- any three of the inputs
- all four inputs
22. If the output of a three-input AND gate must be a logic LOW, what must the condition of the inputs be?
- All inputs must be LOW.
- All inputs must be HIGH.
- At least one input must be LOW.
- At least one input must be HIGH.
23. Logically, the output of a NOR gate would have the same Boolean expression as a(n):
- NAND gate immediately followed by an inverter
- OR gate immediately followed by an inverter
- AND gate immediately followed by an inverter
- NOR gate immediately followed by an inverter
24. A logic probe is placed on the output of a gate and the display indicator is dim. A pulser is used on each of the input terminals, but the output indication does not change. What is wrong?
- The dim indication on the logic probe indicates that the supply voltage is probably low.
- The output of the gate appears to be open.
- The dim indication is the result of a bad ground connection on the logic probe.
- The gate is a tristate device.
25. What is the Boolean expression for a three-input AND gate?
- X = A + B + C
- X = A · B · C
- A – B – C
- A $ B $ C
26. Which of the following gates has the exact inverse output of the OR gate for all possible input combinations?
- NOR
- NOT
- NAND
- AND
27. What is the difference between a 7400 and a 7411 IC?
- 7400 has two four-input NAND gates; 7411 has three three-input AND gates
- 7400 has four two-input NAND gates; 7411 has three three-input AND gates
- 7400 has two four-input AND gates; 7411 has three three-input NAND gates
- 7400 has four two-input AND gates; 7411 has three three-input NAND gates
28. The output of an exclusive-OR gate is HIGH if ________.
- all inputs are LOW
- all inputs are HIGH
- the inputs are unequal
- none of the above
29. A clock signal with a period of 1 s is applied to the input of an enable gate. The output must contain six pulses. How long must the enable pulse be active?
- Enable must be active for 0 s.
- Enable must be active for 3 s.
- Enable must be active for 6 s.
- Enable must be active for 12 s.
30. The AND function can be used to ________ and the OR function can be used to ________ .
- enable, disable
- disable, enable
- enable or disable, enable or disable
- detect, invert