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Question 1

What is sequential logic?

Answer 1

This is a logic circuit which depends on both the current input and previous values of input

Question 2

What is combinational logic?

Answer 2

This is a logic circuit which depends on only the current inputs

Question 3

What is a clock siganl

Answer 3

It is a square wave electrical signal with a frequency called the clock frequency

Question 4

When does a circuit with a clock cycle update?

Answer 4

On a clock edge

Question 5

What are the two clock edges?

Answer 5

> Rising edge / Positive edge

> Falling edge / Negative edge

Question 6

What type of circuit does not use a clock signal?

Answer 6

This is an asynchronous circuit

Question 7

How is a positive clock represented on a logic element?

Answer 7

A triangle into the circuit element.

Looks like: =>

Question 8

How is a negative clock represented on a logic element?

Answer 8

A triangle with a dot into the circuit element.

Looks like: =°>

Question 9

What is a d-latch? (4)

Answer 9

> This is a fundamental sequential logic circuit component
It is bistable
When the enable gate is powered the output will take the value of the input
When the enable gate is not powered the output will hold its value

Question 10

What is an Astable Multivibrator?

Answer 10

A component that oscillates between two values

Question 11

What is a monostable multivibrator?

Answer 11

> A component that can be put into a state but has a single stable state and will return to that stable state after a while of being in a different state
Also called a one-shot

Question 12

What is a D-Flip-Flop? (3)

Answer 12

> A data/delay flip flop
The output is delayed by a lock cycle compared to the change of input
Constructed from D-Latches

Question 13

What are the inputs and outputs?

Answer 13

Inputs
> D - Data
> E - Enable
Outputs
> Q - Stored Value
> NotQ - Inverted stored value

Question 14

What is the truth table for a D-latch?

Answer 14

E D Q   Qnot
0 0 NC NC
0 1  NC NC
1 0  0    1
1 1   1     0

NC - No change

Question 15

What is the circuit for a dlatch?

Answer 15

> 4 NAND logic gates (A topleft, B topright ,C bottomleft, D bottomright)
> Data goes into A
> Enable goes into C and A
> Output of A goes into C
> Output of A goes into B
> Output of C goes into D
> Output of B goes into D
> Output of D goes into B
> Output of B is Q

Question 16

How is a D-flop-flop constructed form D-Latches?

Answer 16

> Data goes into the first master d-Latch and the output goes into the second slave d-latch.
The enable pin is connected into the second d-latch and is inverted with a not gate and goes into the fist d-latch

Question 17

What is the sequential process of a D-Flip-Flop?

Answer 17

> When the clock is low, the master FF is transparent and passes D to Q but the slave is locked
The value of D is stored in the master but it cannot propagate to the output Q because the slave is locked
When the clock goes high, the master locks and the slave unlocks and becomes transparent
The value of in the master Q is passed onto the output Q

Question 18

How can multiple bits be stored?

Answer 18

By grouping D-Flip-Flops

Question 19

What is a register and what is its property?

Answer 19

> Temporary high speed memory

> Fast read and write speeds

Question 20

Why is the size of a register often small?

Answer 20

Because it is expensive

Question 21

Where is the register found?

Answer 21

Inside the CPU

Question 22

What are the two different methods to writing to a register and what does each type mean?

Answer 22

Serial - Writing a single bit at a time

Parallel - Writing all the bits in one go

Question 23

What is Parallel-in/Parallel-out?

Answer 23

> All the FF’s are in parrallel
Each FF shares the same clock signal and keeps the operations synchronous
Each bit from a data bus is fed into an individual FF
All data is written in a single clock cycle

Question 24

What is Serial-in/Serial-out?

Answer 24

> FF are put in series with each other
As the clock changes, bits are shifted along to the next flip flop. This takes time as one bit is loaded per clock cycle.

Question 25

What is a shift register?

Answer 25

These shift data to the left or right

Question 26

Where are shift registers used?

Answer 26

> UARTS

> UARTS are Universal Asynchronous receiver transmitter

Question 27

What happens when you shift a binary number to the left or to the right?

Answer 27

> Left - Multiplies by 2

> Right - Divides by 2

Question 28

How does a shift register function?

Answer 28

> Values are loaded in parallel

> Values are shifted serially

Question 29

What is it called when values are loaded in parallel and shifted serially?

Answer 29

Parallel to serial conversion

Question 30

How can a parallel and shift multipurpose register be controlled?

Answer 30

With an additional control bit to decide the shift of parallel function. This controls a multiplexer.