Roles and components of the Processor

Question 1

What is Machine Code?

Answer 1

Machine code instructions are written in binary code that the processor can interpret and execute

Question 2

What are instruction sets?

Answer 2

The instruction set is the set of the machine code instructions that a particular type of processor can understand and execute.

Question 3

What operations do instruction sets contain?

Answer 3

• Arithmetic operations (ADD, SUB)
• Data transfer operation (MOV, OUT)
• Logical operations (AND, OR)
• Jump operations (JMP, JZ – jump if zero)

Question 4

How many bits are an Opcode?

Answer 4

• 4 bits

Question 5

How many bits are an operand?

Answer 5

12 bits

Question 6

What is an op-code?

Answer 6

Op-code instructions are the part of a machine code instruction that represents a basic machine operation.

Question 7

What is an operand?

Answer 7

Operand is value or memory address that forms part of a machine code instruction.

Question 8

How are Instructions and data are located in memory?

Answer 8

Instructions and data are located in memory by using addressing modes

Question 9

What is immediate addressing?

Answer 9

• Immediate addressing means that the data in the operand is fixed; in other words, it is immediately available for use.
• Typical example: ADD 12 – this instruction could be used to add 12 to the accumulator.

Question 10

What is an advantage of immediate addressing?

Answer 10

This is a very fast addressing mode since the data is readily available, rather than needing to obtain a data value from a memory address.

Question 11

What is Direct Addressing?

Answer 11

• Direct addressing, or absolute addressing, means that the code is directly referred to a memory location.
• Example: ADD (1302) – this instruction adds the contents of memory location (1302) to the accumulator.

Question 12

What is an disadvantage of direct addressing?

Answer 12

The disadvantage of using code that directly refers to memory addresses is that the code cannot be relocated; therefore, it is typically used on single-program systems, such as a car engine fuel control system

Question 13

What is assembly language?

Answer 13

Assembly language is used to make machine code instructions more understandable by using mnemonic codes

Question 14

What is ARM?

Answer 14

ARM is a load-store architecture meaning that memory can only be accessed by:
* Loading from memory into a register
* Storing the result back into memory

Question 15

Explain this example:
LDR r1, #12
ADD r2, r1, #5
SUB r3, r2, #3
STR r3, 1203

Answer 15

Immediate address loads the data without reference to an address
# indicates that the operand is a number
1. Loads the number 12 into the register r1
2. Adds the number 5 to value in r1 and stores result in r2 (making 17)
3. Subtracts the number 3 from value in r2 and stores result in r3 (making 14)
4. Stores the contents of the register r3 (14) into memory address 1203

Question 16

Explain this Direct addressing example:
LDR r1, 12
ADD r2, r1, 13
SUB r3, r2, 14
STR r3, 150

Answer 16

In this case the operand is a memory address
1. Loads data in memory address 12 (4) into r1
2. Adds the data in memory address 13 (5) to r1 and stores result in r2 (making 9)
3. Subtracts the data in memory address 14 (3) from the r2 and stores result in r3 (making 6)
4. Stores the result in r3, which is 4 + 5 – 3 = 6 into memory address 150

Question 17

What is compare used for?

Answer 17

Compare is used to compare two values; the result is normally used as a setup for a conditional jump

Question 18

Explain this compare example?
CMP r1, #23
CMP r1, 23
CMP r1, r2

Answer 18

• compares r1 with the number 23 (immediate addressing).
• compares r1 with the number stored in memory address 23 (direct addressing)
• compares r1 with register r2

Question 19

What is branching?

Answer 19

Branching is used for conditional statements or unconditional statements

Question 20

What is a label?

Answer 20

A label is a sequence of characters that identities a location in computer source code.

Question 21

What is unconditional branching?

Answer 21

Unconditional branching is a command where a section of code is jumped over, with no conditional testing

Question 22

What is conditional branching?

Answer 22

Conditional branching is a command where a section of code is jumped over based on a conditional test

Question 23

What is a logic bitwise operator?

Answer 23

Logical bitwise operator is where a logical operation is carried out on each column of two operands

Question 24

Whhat does in bitwise operations, the ‘#’ symbol mean?

Answer 24

In bitwise operations, the ‘#’ symbol in the instructions below indicates that the operand is a number and so is an example of immediate addressing

Question 25

What is a logic shift?

Answer 25

Logical shift is a bitwise operation where all the bits of an operand are shifted left or right. After the shift operation is completed the vacant-bit positions are filled with zeros.

Question 26

What are the rules of logic shift?

Answer 26

Logical shifts can be useful as efficient ways of performing multiplication or division of unsigned integers by powers of two.
* Shifting left by n bits has the effect of multiplying it by 2n.
* Shifting right by n bits has the effect of dividing it by 2n.

Question 27

What is a Halt?

Answer 27

Halt simply terminates the program operation