Digital Logic Quiz: Truth Tables and Logic Gates

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Questions and Answers

What is the number of input combinations in a two-input truth table?

4 (correct)

What is the purpose of a logic gate?

To design electronic circuits

To create mechanical devices

To implement boolean logic (correct)

To implement analog logic

What determines the actual values for x in a truth table?

The output state

The type of logic circuit (correct)

The binary counting sequence

The number of input combinations

What is the general formula for the number of input combinations in an N-input truth table?

2^N Signup and view all the answers

What is the purpose of a truth table?

To list all possible combinations of input logic levels Signup and view all the answers

What is a logic circuit composed of?

A combination of logic gates Signup and view all the answers

How many entries are there in a four-input truth table?

16 Signup and view all the answers

What is the relationship between the list of all possible input combinations and the binary counting sequence?

They follow the same sequence Signup and view all the answers

What is the building block of all logic circuits?

Logic gates Signup and view all the answers

What is the outcome of the OR operation when both inputs are 0?

X is always 0 Signup and view all the answers

What is the Boolean expression for the OR operation?

X = A + B Signup and view all the answers

What is the result of combining three inputs using the OR operation, where all three inputs are 1?

X = 1 Signup and view all the answers

What is the purpose of the OR operation in logic circuits?

To produce a logic 1 for every combination of input levels where one or more inputs are 1 Signup and view all the answers

What is the difference between the OR operation and ordinary addition in Boolean algebra?

The OR operation produces 1 + 1 = 1, not 1 + 1 = 2 Signup and view all the answers

What is an example of a complex combination of logic circuits?

An integrated circuit Signup and view all the answers

How many basic Boolean operations are learned in digital techniques?

3 Signup and view all the answers

What is the initial value of the R input in the given latch circuit?

Logic 1 Signup and view all the answers

What is the output of the upper NAND gate when the inputs are 0 and 1?

Logic 1 Signup and view all the answers

What is the effect of the output of the lower NAND gate on the upper NAND gate?

It does not affect the output Signup and view all the answers

What is the final state of the Q and Q' outputs after the flip-flop has changed?

Q = 1, Q' = 0 Signup and view all the answers

What is the relationship between the outputs Q and Q' under normal conditions?

They are the inverse of each other Signup and view all the answers

What is the sequence of events that causes the flip-flop to change?

S input goes low, then R input goes high Signup and view all the answers

What is the role of the R input in the given latch circuit?

It provides a high signal to the upper NAND gate Signup and view all the answers

What happens to the outputs Q and Q' when the latch circuit is triggered?

They flip Signup and view all the answers

What is the output expression of an inverter in a logic-circuit diagram?

The input expression with a bar over it Signup and view all the answers

What is the notation used to represent an inverted value in plain text?

A_bar Signup and view all the answers

What is the equation for the circuit on the left in the diagram?

A_bar + B Signup and view all the answers

What is the output of the inverter in the right circuit?

(A + B)_bar Signup and view all the answers

What is the significance of the bar covering the entire expression in the right circuit?

It indicates the entire expression is inverted Signup and view all the answers

What is true about the expressions A + B̄ and A + B?

They are never equal Signup and view all the answers

What is the purpose of using an inverter in a logic circuit?

To invert the input signal Signup and view all the answers

What is the advantage of using a physical bar over the variable in a logic circuit?

It makes the circuit easier to read Signup and view all the answers

What is the primary function of an S-R flip-flop?

To latch the output to either 1 or 0 Signup and view all the answers

What is the name of the circuit shown in the diagram?

S-R flip-flop Signup and view all the answers

What is the meaning of the term 'invalid state' in the context of flip-flops?

When the flip-flop is in a state of limbo Signup and view all the answers

What happens when both inputs of an S-R latch are high?

The latch remains in the last state it was told to switch to Signup and view all the answers

What type of gate is used to construct the S-R flip-flop in the diagram?

NAND gate Signup and view all the answers

What is the purpose of the Q and Q' outputs in an S-R flip-flop?

To output the current state of the flip-flop Signup and view all the answers

What is the name of the type of flip-flop that is also known as an S-R latch?

Set-Reset flip-flop Signup and view all the answers

What happens when an S-R flip-flop is in an invalid state?

The flip-flop may switch to reverse the output states or remain in an existing condition Signup and view all the answers

Study Notes

Truth Tables

A table that lists all possible combinations of input logic levels on the left and the resultant logic level for output x on the right.
The number of input combinations will equal 2N for an N-input truth table.
The actual values for x will depend on the type of logic circuit.

Simple Logic Gates

A logic gate is an ideal representation of a physical electronic device that implements boolean logic.
Logic gates create a logic circuit, which are used in electronic devices, creating integrated circuits and microprocessors.
The building block of all logic circuits is the logic gate.
All logic actions can be analyzed and simplified into basic actions that are called OR gates, AND gates, and NOT gates.

OR Gates

The OR operation combines two logic inputs, A and B, to produce an output, X.
The output is a logic 1 for every combination of input levels where one or more inputs are 1.
The boolean expression for the OR operation is X = A + B.

Inverters in Circuits

An inverter (NOT gate) in a logic-circuit diagram has an output expression equal to the input expression with a bar over it.
The equation for a circuit using an inverter is A_bar + B, where A_bar is the inverted value of A.

Flip-Flops

A flip-flop is a type of logic circuit that can store a bit (a 0 or 1).
Types of flip-flops include Set-Reset (SR) flip-flop, Master-Slave (JK) flip-flop, Data (D) flip-flop, and Toggle (T) flip-flop.
An SR flip-flop can be constructed using two NAND gates.

SR Flip-Flop Operation (NAND)

The SR flip-flop has two inputs, S (Set) and R (Reset), and two outputs, Q and Q'.
The circuit is also known as an S-R latch, where the outputs "latch" to either 1 or 0 based on a pulsed input.
The latch is in an invalid state when both inputs are high.
When S is 0 and R is 1, the latch flips, and Q becomes 1 and Q' becomes 0.

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Description

Test your knowledge of truth tables and simple logic gates, fundamentals of digital logic and electronic devices.