A451: Instructions

Question 1

What are the three parts of an ‘instruction code’?

Answer 1

• Number bit
• Operand
• Op-code

Question 2

Explain what is meant by ‘machine code’ or ‘machine language’.

Answer 2

Machine code or machine language is a system of instructions and data executed directly by the central processing unit of a computer

Question 3

State the format in which the instructions are coded.

Answer 3

The instructions are encoded in binary.

Question 4

What is the name given to the range of instructions that can be executed?

Answer 4

The instruction set.

Question 5

State whether there is a common set of instructions or if each set is unique for each processor or family of processors.

Answer 5

The instructions are unique for each processor type.

Question 6

• Each machine code instruction consists of two fields.

- State the names of each of these fields and the information that they contain.

Answer 6

• The two fields are the opcode and the operand.
• The opcode specifies the operation that is to be performed, e.g. add numbers or store data
  in a register.
• The operand stores the data that is to be used or the register in which it can be found or
  has to be stored.

Question 7

Explain what mnemonics are and why they are used by programmers.

Answer 7

A mnemonic is a word that is used to represent an opcode, as it is difficult for programmers
to remember all of the opcodes in binary format and use them accurately when coding
algorithms.

Question 8

0000 STO

Answer 8

Store data at memory location indicated by the operand.

Question 9

0001 LOAD

Answer 9

Load the number located in the operand.

Question 10

0010 LOAD

Answer 10

Load the number found at the memory location indicated by the operand.

Question 11

0100 ADD

Answer 11

Add the number located in the operand.

Question 12

1000 ADD

Answer 12

Add the number found at the memory location indicated by the operand.

Question 13

Load the number 13.

Answer 13

Opcode Operand

0001 0001101

Question 14

Load the number found at memory location 6

Answer 14

Opcode Operand

0010 00000110

Question 15

Add the number 113.

Answer 15

Opcode Operand

0100 01110001

Question 16

Load the number 10, add the number 21 and store the result at memory location 30.

Answer 16

Opcode Operand
0001 00001010
0100 00010101
0000 00011110

Question 17

State the data that would be found at memory location 30.

Answer 17

000011111

Question 18

Explain what is meant by an opcode? (2)

Answer 18

An opcode is the portion of amachine language instruction (1) that specifies the operation to be performed by a microprocessor. (1)

Question 19

Explain what is meant by an operand? (2)

Answer 19

The operand contains either the data that has to used in an operation (1) or a memory address where data can be found or stored. (1)

Question 20

How is the information contained in opcodes and operands coded?

Answer 20

In binary format.

Question 21

State the name for the words that programmers use to represent opcodes.

Answer 21

Mnemonics.

Question 22

Explain how instructions are coded as bit patterns?

Answer 22

• Programming instructions are compiled into binary to turn on the correct parts of the CPU circuitry

Question 23

Describe CPU?

Answer 23

The CPU is a complex combination of circuits to provide logic.

Question 24

How do logical operations work?

Answer 24

Each logical operation is given a binary code. Example 1000 Add.

Question 25

Explain how the computer distinguishes between instructions and data

Answer 25

• Data is separated in memory into different spaces, becasue of the fact that data is inseparable from the binary for the instruction