P2 T2 L11 - Assembly Language Flashcards
Computers can only process instructions that are written in ________ ______.
machine code
A machine code instruction has an ______ and an ______.
opcode (operation code)
operand
Assembly language uses ___________ to represent operation codes and addresses.
mnemonics
All the instructions for a given CPU form its ___________ ___.
instruction set
The assembly code instructions are unique to a given __________ __________.
computer architecture
LDR Rd, < memory ref >
What does it mean?
1 point
- Load the value stored in < memory ref > into register d
STR Rd, < memory ref >
What does it mean?
1 point
- Store the value in register d into memory location specified by < memory ref >
ADD Rd, Rn, < operand >
What does it mean?
1 point
- Add the value specified in < operand > to the value in register n and store the result in register d
SUB Rd, Rn, < operand >
What does it mean?
1 point
- Subtract the value specified by < operand > from the value in register n and store the result in register d
MOV Rd, < operand >
What does it mean?
1 point
- Copy the value specified by < operand > into register d
What could < operand > be?
2 things
- an actual value, specified by #
OR
- a value stored in another register specified by R
In the instruction SUB R3, R2, #5 what type of addressing does it use?
(1 point)
- uses immediate addressing, i.e. the instruction uses the actual value 5 as the operand
In the instruction LDR R1, 300 what type of addressing does it use?
(1 point)
- uses direct addressing, i.e. the instruction uses the memory address (300) holding the value as the operand
In assembly language, there are no IF statements. What do they use instead?
(2 things)
- Compare instruction
2. Branch instruction
CMP Rn, < operand >
What does it mean?
1 point
- Compare the value stored in register n with the value specified by < operand >
B < label >
What does it mean?
1 point
- Always branch to the instruction at position < label> in the program
B< condition >
< label >
What does it mean?
(2 points)
- 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
How are while loops done in assembly language?
2 points
- The equivalent of a WHILE loop can be written using Compare and Branch instructions
- 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
List the logical bitwise operations in assembly language
6 of them
- AND
- ORR also known as OR
- EOR also known as XOR
- MVN also known as NOT
- LSL
- LSR
what does AND do
1 point
- 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
what does ORR do
1 point
- 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
What does EOR do
1 point
- 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
What does MVN do?
1 point
- 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
What does LSL do?
1 point
- 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
What does LSR do?
1 point
- 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
Define operator (1 point)
- an operator is a character or characters that determine the action that is to be performed or considered
Define operand (1 point)
- the operand is the data or memory location used to execute a certain instruction
Define opcode (1 point)
- The opcode is the instruction that is executed by the CPU
Define direct addressing (1 point)
- A way of addressing memory, it means that the operand of an instruction refers directly to a location in memory
Define immediate addressing (1 point)
- 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.
What is HLT
1 point
- HLT (halt) is an assembly language instruction which halts the central processing unit (CPU) until the next external interrupt is fired.
