ASComputer ScienceCambridge (CIE)Exam Questions4. Processor FundamentalsAssembly Language

Assembly Language (Cambridge (CIE) AS Computer Science): Exam Questions

Exam code: 9618

32 mins7 questions
15 marks

The following table shows part of the instruction set for a processor. The processor has two registers, the Accumulator (ACC) and the Index Register (IX).

Instruction

Explanation

Opcode

Operand

LDM

#n

Immediate addressing. Load the number n to ACC

LDD

<address>

Direct addressing. Load the contents of the location at the given address to ACC

LDI

<address>

Indirect addressing. The address to be used is at the given address. Load the contents of this second address to ACC

LDX

<address>

Indexed addressing. Form the address from <address> + the contents of the index register. Copy the contents of this calculated address to ACC

LDR

#n

Immediate addressing. Load the number n to IX

ADD

#n/Bn/&n

Add the number n to the ACC

ADD

<address>

Add the contents of the given address to the ACC

SUB

#n/Bn/&n

Subtract the number n from the ACC

SUB

<address>

Subtract the contents of the given address from the ACC

INC

<register>

Add 1 to the contents of the register (ACC or IX)

DEC

<register>

Subtract 1 from the contents of the register (ACC or IX)

<address> can be an absolute or a symbolic address
# denotes a denary number, e.g. #123 B
denotes a binary number, e.g. B01001010
& denotes a hexadecimal number, e.g. &4A

The current contents of memory are shown:

Address

Data

19

25

20

23

21

2

22

4

23

15

24

50

25

22

The current contents of the ACC and IX are shown:

ACC

50

IX

20

Complete the table by writing the content of the ACC and the IX after each set of instructions has run.

Instructions

ACC content

IX content

1

LDM #19
DEC ACC

2

LDD 23
ADD 19

3

LDI 25
INC ACC

4

LDR #21
LDX 2

How did you do?

23 marks

The following table shows part of the instruction set for a processor. The processor has two registers, the Accumulator (ACC) and the Index Register (IX).

Instruction

Explanation

Opcode

Operand

LDM

#n

Immediate addressing. Load the number n to ACC

LDD

<address>

Direct addressing. Load the contents of the location at the given address to ACC

LDI

<address>

Indirect addressing. The address to be used is at the given address. Load the contents of this second address to ACC

LDX

<address>

Indexed addressing. Form the address from <address> + the contents of the index register. Copy the contents of this calculated address to ACC

LDR

#n

Immediate addressing. Load the number n to IX

ADD

#n/Bn/&n

Add the number n to the ACC

ADD

<address>

Add the contents of the given address to the ACC

SUB

#n/Bn/&n

Subtract the number n from the ACC

SUB

<address>

Subtract the contents of the given address from the ACC

INC

<register>

Add 1 to the contents of the register (ACC or IX)

DEC

<register>

Subtract 1 from the contents of the register (ACC or IX)

<address> can be an absolute or a symbolic address
# denotes a denary number, e.g. #123 B
denotes a binary number, e.g. B01001010
& denotes a hexadecimal number, e.g. &4A

The current contents of memory are shown:

Address

Data

50

54

51

55

52

50

53

52

54

100

55

25

56

50

The current contents of the ACC and IX are shown:

ACC

50

IX

45

Complete the table by writing the content of the ACC after each program has run.

Instructions

ACC content

1

LDD 50
ADD #4
ADD 54

2

LDI 53
DEC ACC
ADD 56

3

LDM #55
SUB #5

How did you do?

34 marks

The following table shows part of the instruction set for a processor. The processor has two registers: the Accumulator (ACC) and an Index Register (IX).

Instruction

Explanation

Opcode

Operand

LDM

#n

Immediate addressing. Load the number n to ACC

LDD

<address>

Direct addressing. Load the contents of the location at the given address to ACC

LDI

<address>

Indirect addressing. The address to be used is at the given address. Load the contents of this second address to ACC

LDX

<address>

Indexed addressing. Form the address from <address> + the contents of the index register. Copy the contents of this calculated address to ACC

LDR

#n

Immediate addressing. Load the number n to IX

ADD

#n/Bn/&n

Add the number n to the ACC

ADD

<address>

Add the contents of the given address to the ACC

SUB

#n/Bn/&n

Subtract the number n from the ACC

SUB

<address>

Subtract the contents of the given address from the ACC

INC

<register>

Add 1 to the contents of the register (ACC or IX)

<address> can be an absolute or a symbolic address
# denotes a denary number, e.g. #123 B
denotes a binary number, e.g. B01001010
& denotes a hexadecimal number, e.g. &4A

The current contents of memory are shown:

Address

Data

19

24

20

2

21

1

22

3

23

5

24

4

25

22

The current contents of the ACC and IX are shown:

ACC

12

IX

1

Complete the table by writing the content of the ACC after each program has run.

Program number

Instructions

ACC content

1

LDD 20
ADD #2

2

LDX 22

3

LDI 25
INC ACC
SUB 22

4

LDD 19
LDM #5
LDM #25

How did you do?

44 marks

The following table shows part of the instruction set for a processor. The processor has two registers: the Accumulator (ACC) and an Index Register (IX).

Instruction

Explanation

Opcode

Operand

LDM

#n

Immediate addressing. Load the number n to ACC

LDD

<address>

Direct addressing. Load the contents of the location at the given address to ACC

LDI

<address>

Indirect addressing. The address to be used is at the given address. Load the contents of this second address to ACC

LDX

<address>

Indexed addressing. Form the address from <address> + the contents of the index register. Copy the contents of this calculated address to ACC

LDR

#n

Immediate addressing. Load the number n to IX

ADD

#n/Bn/&n

Add the number n to the ACC

ADD

<address>

Add the contents of the given address to the ACC

SUB

#n/Bn/&n

Subtract the number n from the ACC

SUB

<address>

Subtract the contents of the given address from the ACC

INC

<register>

Add 1 to the contents of the register (ACC or IX)

<address> can be an absolute or a symbolic address
# denotes a denary number, e.g. #123 B
denotes a binary number, e.g. B01001010
& denotes a hexadecimal number, e.g. &4A

The current contents of memory are shown:

Address

Data

10

1

11

3

12

5

13

11

14

10

15

16

16

12

The current contents of the ACC and IX are shown:

ACC

10

IX

0

Complete the table by writing the content of the ACC after each program has run.

Program number

Instructions

ACC content

1

LDI 15
SUB #1

2

LDD 14
ADD 11

3

LDM #11
ADD #3
SUB 16

4

LDR #2
LDX 14
ADD #2

How did you do?

54 marks

The following table shows part of the instruction set for a processor. The processor has two registers: the Accumulator (ACC) and an Index Register (IX).

Instruction

Explanation

Opcode

Operand

LDM

#n

Immediate addressing. Load the number n to ACC

LDD

<address>

Direct addressing. Load the contents of the location at the given address to ACC

LDI

<address>

Indirect addressing. The address to be used is at the given address. Load the contents of this second address to ACC

LDX

<address>

Indexed addressing. Form the address from <address> + the contents of the index register. Copy the contents of this calculated address to ACC

LDR

#n

Immediate addressing. Load the number n to IX

ADD

#n/Bn/&n

Add the number n to the ACC

ADD

<address>

Add the contents of the given address to the ACC

SUB

#n/Bn/&n

Subtract the number n from the ACC

SUB

<address>

Subtract the contents of the given address from the ACC

INC

<register>

Add 1 to the contents of the register (ACC or IX)

<address> can be an absolute or a symbolic address
# denotes a denary number, e.g. #123 B
denotes a binary number, e.g. B01001010
& denotes a hexadecimal number, e.g. &4A

The current contents of memory are shown:

Address

Data

48

51

49

6

50

48

51

50

52

49

53

50

54

6

The current contents of the ACC and IX are shown:

ACC

2

IX

50

Complete the table by writing the content of the ACC after each program has run.

Program number

Instructions

ACC content

1

LDM #50
INC ACC
SUB #1

2

LDI 51
ADD 52

3

LDR #2
LDX 50
DEC ACC

4

LDD 52
SUB 54
INC ACC

How did you do?

6a1 mark

Identify the purpose of the first pass of a two-pass assembler.

How did you do?

6b6 marks

The following table shows part of the instruction set for a processor. The processor has two registers, the Accumulator (ACC) and the Index Register (IX).

Instruction

Explanation

Opcode

Operand

LDR

#n

Immediate addressing. Load the number n to IX

STO

<address>

Store contents of ACC at the given address

ADD

<address>

Add the contents of the given address to the ACC

INC

<register>

Add 1 to the contents of the register (ACC or IX)

CMP

#n

Compare the contents of ACC with number n

JPE

<address>

Following a compare instruction, jump to <address> if the compare was True

OUT

Output to the screen the character whose ASCII value is stored in ACC

<address> can be an absolute or symbolic address

# denotes a denary number, e.g. #123

(i) Give one example of an instruction that belongs to each of the following instruction groups.

Only use the instructions given in the table. Each instruction must have a suitable operand.

Data movement ...........................

Arithmetic operation ...................

Conditional instruction ................

(3)

(ii) The instruction LDR #2 uses immediate addressing.

Give one similarity and one difference between direct addressing and indexed addressing.

(2)

(iii) Identify one other mode of addressing.

(1)

How did you do?

7a4 marks

The following table shows part of the instruction set for a processor. The processor has two registers, the Accumulator (ACC) and the Index Register (IX).

Instruction

Explanation

Opcode

Operand

LDD

<address>

Direct addressing. Load the contents of the location at the given address to ACC

LDX

<address>

Indexed addressing. Form the address from <address> + the contents of the index register. Copy the contents of this calculated address to ACC

LDR

#n

Immediate addressing. Load the number n to IX

STO

<address>

Store the contents of ACC at the given address

ADD

#n

Add the denary number n to the ACC

JMP

<address>

Jump to the given address

INC

<register>

Add 1 to the contents of the register (ACC or IX)

CMP

<address>

Compare the contents of ACC with the contents of <address>

CMI

<address>

Indirect addressing. The address to be used is at the given address. Compare the contents of ACC with the contents of this second address

JPE

<address>

Following a compare instruction, jump to <address> if the compare was True

IN

Key in a character and store its ASCII value in ACC

OUT

Output to the screen the character whose ASCII value is stored in ACC

END

Return control to the operating system

<address> can be an absolute or a symbolic address
# denotes a denary number, e.g. #123

The instructions in the processor’s instruction set can be grouped according to their function.

Identify the instruction group for each of the following opcodes.

IN .............................

ADD .........................

JPE ...........................

CMI ...........................

How did you do?

7b1 mark

The current contents of main memory and selected values from the ASCII character set are given on page 15.

Trace the program currently in memory using the trace table when the input is ‘1’.

Table with computer instructions, memory addresses, and ASCII values. Includes instruction and output columns, memory values for addresses 100-111.

How did you do?