Chapter 43 - Adders and D-type flip-flops

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Total cards: 24•Content version: v4•Public deck•Updated: 8/1/2026

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Front (Question)

Is it possible to output the results of a binary addition or subtraction?

Back (Answer)

» Yes with the right combination of gates

Front (Question)

What is a half adder?

Back (Answer)

» An adder performs binary addition and subtraction

Front (Question)

What is the purpose of a half adder?

Back (Answer)

» Performs addition of 2bits

Front (Question)

How many inputs and outputs does a half adder produce?

Back (Answer)

» Takes an input of 2 bits of A and B and outputs results S and carry C

Front (Question)

What gates does a half-adder consist of?

Back (Answer)

» XOR gate » AND gate

Front (Question)

What does S represent?

Back (Answer)

» The sum and is equal to A XOR B

Front (Question)

What does C represent?

Back (Answer)

» Represents the Carry and is equal to A AND B

Front (Question)

What are the disadvantages of a half adder?

Back (Answer)

» Can only add one bit » No third input so cannot use the carry from a previous addition to add n bit numbers

Front (Question)

If A and B was both 1, what is the value of S and C in a half adder?

Back (Answer)

» S = 0 » C = 1

#10

Front (Question)

What is a full adder?

Back (Answer)

» Consists of 2 half adders to add three bits together including the inputs A and B and a Carry bit

#11

Front (Question)

How many inputs and output does a full adder have?

Back (Answer)

» Has 3 inputs, A, B, and C(in) » 2 outputs, the SUM(S) and C(out)

#12

Front (Question)

What gates does the full adder consist of?

Back (Answer)

» 2 XOR GATES » 2 AND GATES » 1 OR GATE » 2 half adders and 1 OR

#13

Front (Question)

What is the boolean logic of S and C(out) in a full adder?

Back (Answer)

» S = (A XOR B) XOR C(in) » C(out) = ((A XOR B) AND C ) OR ( A AND B)

#14

Front (Question)

What does concatenating full adders do?

Back (Answer)

» Can be connected to make n full adders » Can input the carry bit into a subsequent adder along with the 2 new inputs

#15

Front (Question)

How can you simply add the adders together?

Back (Answer)

» Draw a diagram, with A0, B0, S0 and so on » Then simply add the values and where appropriate carry a single bit

#16

Front (Question)

What is a flip flop?

Back (Answer)

» An elemental sequential logic circuit that can store on bit and flip between 2 states, 0 and 1

#17

Front (Question)

» How many inputs does a D - Type flip flop have?

Back (Answer)

» 2 inputs one called D » Other one called clock signal input

#18

Front (Question)

What is the clock?

Back (Answer)

» Or also known as the oscillator is another type of sequential circuit that changes state at regular time intervals

#19

Front (Question)

Why is the clock needed?

Back (Answer)

» Needed to synchronise the change of state of flip flop circuit

#20

Front (Question)

What is the clock perod?

Back (Answer)

» The time between the 2 rising edge

#21

Front (Question)

What is the clock width?

Back (Answer)

» The width between the rising edge, and falling edge

#22

Front (Question)

When can the D- type flip flop only change states?

Back (Answer)

» Changes on the rising edge of of the clock signal

#23

Front (Question)

What does the D stand for in D-type flip flop?

Back (Answer)

» D stands for Data or Delay

#24

Front (Question)

What does it mean by a positive edge triggered flip flop?

Back (Answer)

» Can only change the output value from 1 to 0