Section A

Question 1

Define ‘synthesis’

Answer 1

“Generation of a circuit model starting from a less abstract one: a transformation between two model views (e.g. Behavioural –> Structural)”

Question 2

What are the three Model Abstraction Levels?

Answer 2

1. Architectural (performs operations)
2. Logic (evaluates logic functions)
3. Geometrical (set of geometrical entities)

Question 3

Define ‘model’

Answer 3

“Representation that shows relevant features without associated details”

Question 4

What is the ‘RTL’?

Answer 4

“Register Transfer Level” : design level of abstraction below behavioural but above structural, using a subset of the HDL.
Events are defined in terms of clocks.

Question 5

How many bits are in a single precision floating point number?

Answer 5

32 bits

Question 6

List the bit numbers and what they relate to in a single precision floating point number:

Answer 6

23 bits: 0 - 22: Mantissa/Fraction
8 bits: 23 - 30: Exponent
1 bit: 31: Sign

Question 7

What is the need for Wireload Models (WLMs)?

Answer 7

To model and investigate the interconnect delays at higher levels of design.

Question 8

What is responsible for interconnect delay?

Answer 8

Interconnect capacitance (wiring+routing), and interconnect resistance.

Question 9

Which factors, in combination, produce the Total Delay for DSM circuits?

Answer 9

1. Delay due to wires

2. Delay due to cells

Question 10

What causes wire delays in DSM circuits?

Answer 10

The Resistance.Capacitance (RC) Coefficient (assume => 8ns)

Question 11

ANSI/IEEE Floating Point:

Answer 11

• Biased Exponent
• No leading zeros
• Implied most significant 1 in the mantissa
• Binary point of mantissa is immediately after most significant 1
• Stored part of mantissa is only fractional part

Question 12

What is the motivation for using Floating Point notation?

Answer 12

Allows representation of very small and very large numbers, which is otherwise restricted with fixed point notation (only integers).

Question 13

How can Floating Point be compared to scientific notation?

Answer 13

e.g. 10011101 = 1.0011101 x 2^7

first 1 not stored as assumed present, mantissa = 0011101, exponent = 111

Question 14

What is the exponent biases in floating point?

Answer 14

Single: +127 (2^(8-1) - 1)
Double: +1023 (2^(11-1) -1)

Question 15

How is each decimal digit represented in BCD?

Answer 15

Each digit is represented by a four bit binary code that varies from 0000 - 1001 (0 to 9)

Question 16

If correction is required in BCD, which number do we add and why?

Answer 16

• Add 0110 (decimal 6)

- This produces a carry to by-pass the invalid codes (i.e. 15 - 9 = 6)

Question 17

What is the defining feature of Gray Code?

Answer 17

Only one bit changes state when transitioning between adjacent codewords in the sequence

Question 18

What is the purpose of a parity bit?

Answer 18

Error detection: A parity bit, or check bit is a bit added to the end of a string of binary code that indicates whether the number of bits in the string with the value ‘1’ is even or odd.

N.B. When added to given set of bits:

‘Even Parity Bits’ ensure that total number of 1s in result is even.

‘Odd Parity bits’ ensure that total number of 1s in result is odd.

Question 19

What is the Datapath?

Answer 19

The Datapath is the core of the processor, where computations are performed.

Consists of interconnection of basic combinational functions (e.g. Arithmetic Operations/Logic operators)

Question 20

What makes up a Generic Digital Processor?

Answer 20

Datapath, Memory, Control, Input/Output

Question 21

What is the purpose of Memory in a Generic Digital Processor?

Answer 21

To store results or fetch data

Question 22

What is the purpose of Control in a Generic Digital Processor?

Answer 22

To determine what will happen next in the cycle

Question 23

How to convert a positive binary number to a negative 2’s C?

Answer 23

1. Invert all bits of positive number
2. Add 1

e.g. +5
0101 -> 1010 -> 1011 = (-5)

Question 24

Why is 2’s C used almost universally?

Answer 24

The same hardware (invert, add) can be used for addition and subtraction

Question 25

What is an FSM?

Answer 25

Finite State Machine: Any device/computational model that can be in one of a number of finite states at any time.