4.5 - Logic Gates

Question 1

What is the XOR gate and what is its output? Draw it:

Answer 1

Exclusive OR gate
If one but not both of the inputs is 1 the output is 1, otherwise the output is 0
OrR gate with a line through the wires (check)

Question 2

What is the NAND gate and what is its output? Draw it:

Answer 2

Combination of AND and NOT
Inverts the output of the And gate
AND gate with a dot then line for the output wire

Question 3

What is the NOR gate and what is its output? Draw it:

Answer 3

Inverse the OR gate
Output is 1 only if both the inputs are 0
OR gate with a dot and then a wire for the output

Question 4

What is the universal gate?

Answer 4

NAND as it combines the functions of two gates (AND, NOT) into a single gate
Different combinations of NAND can act like OR, NOT, AND gates
Any circuit can be built just by NAND

Question 5

Advantages of NAND gates?

Answer 5

Minimises cost of production if only NAND is needed
Speed up processing

Question 6

What are adders?

Answer 6

A logic circuit that can be used to add Boolean values together
Two types: half and full

Question 7

What are half adders?

Answer 7

A logic circuit with two inputs, two outputs and two logic gates (XOR and AND)
Used to add two Boolean values

Question 8

What is a full adder?

Answer 8

Has three inputs and two outputs, enables it to input two Boolean values and a carry bit from previous, less significant operation

Question 9

What is an edge-triggered D-type flip-flop?

Answer 9

A logic circuit which can be used as a memory unit for storing the value of a single bit

Question 10

What does an edge-triggered D-type flip-flop include?

Answer 10

Has two inputs, one for data and another for a clock signal, one output which always holds the value of the stored bit

Question 11

What is a logic gate?

Answer 11

Devices which apply logical operations to one or more Boolean inputs in order to produce a single output