P2 T2 L11 - Assembly Language

Question 1

Computers can only process instructions that are written in ________ ______.

Answer 1

machine code

Question 2

A machine code instruction has an ______ and an ______.

Answer 2

opcode (operation code)

operand

Question 3

Assembly language uses ___________ to represent operation codes and addresses.

Answer 3

mnemonics

Question 4

All the instructions for a given CPU form its ___________ ___.

Answer 4

instruction set

Question 5

The assembly code instructions are unique to a given __________ __________.

Answer 5

computer architecture

Question 6

LDR Rd, < memory ref >

What does it mean?
1 point

Answer 6

1. Load the value stored in < memory ref > into register d

Question 7

STR Rd, < memory ref >

What does it mean?
1 point

Answer 7

1. Store the value in register d into memory location specified by < memory ref >

Question 8

ADD Rd, Rn, < operand >

What does it mean?
1 point

Answer 8

1. Add the value specified in < operand > to the value in register n and store the result in register d

Question 9

SUB Rd, Rn, < operand >

What does it mean?
1 point

Answer 9

1. Subtract the value specified by < operand > from the value in register n and store the result in register d

Question 10

MOV Rd, < operand >

What does it mean?
1 point

Answer 10

1. Copy the value specified by < operand > into register d

Question 11

What could < operand > be?

2 things

Answer 11

1. an actual value, specified by #

OR

2. a value stored in another register specified by R

Question 12

In the instruction SUB R3, R2, #5 what type of addressing does it use?
(1 point)

Answer 12

1. uses immediate addressing, i.e. the instruction uses the actual value 5 as the operand

Question 13

In the instruction LDR R1, 300 what type of addressing does it use?
(1 point)

Answer 13

1. uses direct addressing, i.e. the instruction uses the memory address (300) holding the value as the operand

Question 14

In assembly language, there are no IF statements. What do they use instead?
(2 things)

Answer 14

1. Compare instruction

2. Branch instruction

Question 15

CMP Rn, < operand >

What does it mean?
1 point

Answer 15

1. Compare the value stored in register n with the value specified by < operand >

Question 16

B < label >

What does it mean?
1 point

Answer 16

1. Always branch to the instruction at position < label> in the program

Question 17

B< condition >
< label >

What does it mean?
(2 points)

Answer 17

1. Conditionally branch to if the last comparison met the conditions specified by :

2. < condition > can be:
EQ: equal to 0
NE: not equal to 0
GT: greater than
LT: less than

e.g. BEQ, BNE, BGT, BLT

Question 18

How are while loops done in assembly language?

2 points

Answer 18

1. The equivalent of a WHILE loop can be written using Compare and Branch instructions
2. A CMP is followed by a branch
   e. g

MOV R1, #0 ;initialise R1 to hold total
LOOP
INPUT R0 ;input a number
ADD R1, R1, R0 ;add number to R1
CMP R0, #0 ; compare number with 0
BNE LOOP ; branch if not zero
STT R1, 100 ; store total in location 100

Question 19

List the logical bitwise operations in assembly language

6 of them

Answer 19

1. AND
2. ORR also known as OR
3. EOR also known as XOR
4. MVN also known as NOT
5. LSL
6. LSR

Question 20

what does AND do

1 point

Answer 20

1. returns 1 if both bits are 1 - result stored in Rd
   e. g.

Rd 1 0 1 0 1 0 1 0
Rn 1 1 1 1 0 0 1 1
AND Rd, Rn 1 0 1 0 0 0 1 0

Question 21

what does ORR do

1 point

Answer 21

1. returns 1 if one or both bits are 1 - result stored in Rd
   e. g.

Rd 1 0 1 0 1 0 1 0
Rn 1 1 1 1 0 0 1 1
ORR Rd, Rn 1 1 1 1 1 0 1 1

Question 22

What does EOR do

1 point

Answer 22

1. returns 1 if one (but not both) bit is 1 - result stored in Rd

Rd 1 0 1 0 1 0 1 0
Rn 1 1 1 1 0 0 1 1
EOR Rd, Rn 0 1 0 1 1 0 0 1

Question 23

What does MVN do?

1 point

Answer 23

1. change 1 to 0 and 0 to 1

Rd 1 0 1 0 1 0 1 0
MVN Rd 0 1 0 1 0 1 0 1

Question 24

What does LSL do?

1 point

Answer 24

1. Logical Shift Left - shifts all the bits left a specified number of spaces
   e. g.

Rn 1 0 1 0 1 0 1 0
LSL Rd, Rn, #2 1 0 1 0 1 0 0 0

Vacated spaces filled with 0

Nb Rn is the starting point in this example - look at instruction format

Question 25

What does LSR do?

1 point

Answer 25

1. Logical shift right - shifts all the bits right a specified number of places

Rn 1 0 1 0 1 0 1 0
LSR Rd, Rn, #2 0 0 1 0 1 0 1 0

vacated spaces filled with 0
Nb Rn is the starting point in this example

Question 26

Define operator (1 point)

Answer 26

1. an operator is a character or characters that determine the action that is to be performed or considered

Question 27

Define operand (1 point)

Answer 27

1. the operand is the data or memory location used to execute a certain instruction

Question 28

Define opcode (1 point)

Answer 28

1. The opcode is the instruction that is executed by the CPU

Question 29

Define direct addressing (1 point)

Answer 29

1. A way of addressing memory, it means that the operand of an instruction refers directly to a location in memory

Question 30

Define immediate addressing (1 point)

Answer 30

1. Immediate addressing means that the data to be used is hard-coded into the instruction itself.

For instance: ADD 7. Nothing needs to be fetched from memory.

Question 31

What is HLT

1 point

Answer 31

1. HLT (halt) is an assembly language instruction which halts the central processing unit (CPU) until the next external interrupt is fired.