Chapter 3 - Assembly

Question 1

Special Purpose Registers

Answer 1

IP
SP 
Flags
CS
DS
ES
FS
GS

Question 2

IP

Answer 2

instruction pointer; points to next sequential instruction

Question 3

SP

Answer 3

stack pointer; addresses stack area

Question 4

flags

Answer 4

collection of control properties

12 bits

Question 5

C flag

Answer 5

carry flag; holds the carry after addition or borrow after subtraction

Question 6

Z flag

Answer 6

zero flag; reports the result of an arithmetic operation as zero

Question 7

S flag

Answer 7

sign flag; holds the sign of the result after an arithmetic or logic instruction

Question 8

O flag

Answer 8

overflow flag; indicates overflow as a result from signed arithmetic operations

Question 9

CS

Answer 9

code segment; holds the programs used by the system

Question 10

DS

Answer 10

data segment; contains most of the data used by program

data accessed by offset address

Question 11

ES

Answer 11

extra segment; an additional data segment

Question 12

SS

Answer 12

stack segment; defines the are of memory used for the stack.

Stack pointer register determines entry point in stack segment

Question 13

FS & GS

Answer 13

additional segment registers

Question 14

Real mode

Answer 14

allows the microprocessor to only address the 1st MB of memory. any program can access any area of memory

Question 15

offset address

Answer 15

used to select a location within a 64kb segment to address a given program

Question 16

Assembler start of program

Answer 16

.Model small
.stack 100h
Main PROC

mov ax, @data
mov ds, ax

Question 17

Register Addressing

Answer 17

transfers a copy of a byte or word from one register to another

ex: mov ax, bx

Question 18

Immediate addressing

Answer 18

transfers the source immediate byte (actual value) into a register or memory location

ex: mov ah, 0

Question 19

Direct addressing

Answer 19

moves a byte or word between memory and AL, AX, or EAX registers ONLY

most operands must be the same size

ex: count DW 100H
temp DB 20

mov ax, count (or mov count, ax)
mov al, temp (or vice versa)

Question 20

Displacement addressing

Answer 20

almost identical to direct addressing except instruction is 4 bytes wide instead of 3 bytes wide

Question 21

How to move 8 bits into 16 bit register

Answer 21

2 moves

mov al, temp
mov ah, 00h

Question 22

MOV operations allowed

Answer 22

all moves require the source and destination to be of the same size

memory to register; yes (and vice versa)
x bit register to x bit register; yes
x bit register to y bit register; no if x != y
literal to memory; yes
memory to memory; no

Question 23

_GetCh

Answer 23

grabs char from input. result in BL register

Question 24

_GetDate

Answer 24

grabs date.

DL = day
DH = month
CX = year
AL = day of week

Question 25

Binary subtraction for A - B

Answer 25

= A + twos_complement(B)

Question 26

Twos Complement

Answer 26

flip the bits and add 1

Question 27

Size of number as a result of multiplication

Answer 27

8 bit * 8 bit = 16 bit

16 bit * 16 bit = 32 bit

Question 28

Multiplication operations

Answer 28

MUL; unsigned number multiplication

IMUL; signed number multiplication

Question 29

Multiplication operation structure

Answer 29

register/memory location * al/ax

ex: C = A * B

A DW 10
B DW 5
C DW ?

mov ax, B
mul A (or IMUL A)

if C <= 16 bits answer in AX
else
AX = lower 16 bits
DX = remaining upper bits

Question 30

CBW

Answer 30

convert byte to word

sign extend a bye into a word

Question 31

CWD

Answer 31

convert word to double

sign extend word to double word

Question 32

Size of number as a result of division

Answer 32

16 bits / 8 bits = 8 bits

32 bits / 16 bits = 16 bits

Question 33

Division Operations

Answer 33

DIV; unsigned number division

IDIV; signed number division

Question 34

Division Operation Structure

Answer 34

register or eax or ax / reg or mem location

ex: Q = B/C

Q DW ?
R DW ?
B DW 12
C DW 4

mov Ax, B
CWD  (make AX into EAX)
DIV C (or IDIV)

AX = quotient
DX = remainder

Question 35

Jump types

Answer 35

JE --> jump equals
JNE --> jump not equals
JL --> jump less than
JG --> jump greater than
JGE --> jump greater than or equal
JNGE --> jump not greater than or equal
JLE --> jump less than or equal
JNLE --> jump not less than or equal
JMP --> unconditional jump

Question 36

What happens when jump instruction is called?

Answer 36

if the criteria is true, then the program jumps to the specified label

Question 37

What does CALL do?

Answer 37

pushes IP on to stack

replaces current address of IP with address of subprogram

Question 38

What does RET do?

Answer 38

pops the return address from the stack into IP plus the number of bytes specified

Question 39

What happens to begin each subprogram?

Answer 39

save the current bp, set sp equal to bp

Question 40

How to add subprogram parameters?

Answer 40

Parameters pushed on stack from left to right. First parameter located at word ptr [bp + 4], the second at word ptr [bp + 6] etc. (the IP at [bp+2]

Question 41

Where are local variables in the stack frame?

Answer 41

at word ptr [bp-2], word ptr [bp -4] etc.