Executing and Linking an
assembly program
Lesson plan
Review
 Program logic and control
 Practice exercise
 Assembling, Linking and Executing
Programs
 Practice exercise

Review
IMUL register/memory
If operand is a byte
AX= AL * operand

Review
MOV CX, 10
BEGINLOOP
DEC CX
JNZ BEGINLOOP
OR
MOV CX, 10
BEGINLOOP
LOOP BEGINLOOP
Program logic and control

Address: distance from the current
address
Short: distance from -128 to 127 bytes
 Near: -32768 to 32767 bytes
 Far: distance over 32K for the same segment
address or in another segment

Transfer operations
JMP
Unconditional. Transfer control under all
circumstances
Syntax:
[label:] JMP short/near/far address

Transfer operations
Backward jump
BEGINLOOP:
….
JMP BEGINLOOP
Forward jump
JMP STARTLOOP

STARTLOOP:
….
Practice with JMP instruction
Write a program to continuously add 1 to AX
and add AX to BX
(Initially, assign AX and BX any values)
Loop instruction
Loops a specified number of times
Initial value is stored in CX
Each iteration, LOOP deducts 1 from CX.
If CX is not zero, control jumps to the
address specified
Otherwise, finish the loop
 Syntax:

[label:] LOOP short-address
CMP Instruction
[label:] CMP register/memory,
register/memory/immediate
 Compares the first to the second operand
 Affects: AF, CF, OF, PF, SF and ZF flag

CMP AX, DX
JE Startloop
Conditional Jump instructions
Jump based on unsigned data
[label:] JE/JZ
short-address
Jump if equal or Jump if zero
[label:] JNE/JNZ short-address
Jump if not equal or Jump if not zero

Flag: ZF
Example
MOV AL, 5
CMP AL, 5
JE label1
JMP exit
label1: MOV CX, BX
exit:
…..
Conditional Jump instructions
JG: Jump if first operand is Greater then
second operand (as set by CMP
instruction). Signed.
if (ZF = 0) and (SF = OF) then jump
Syntax: [label:] JG
short-address
Example
MOV AL, 5
CMP AL, -5
JG label1
JMP exit
label1: MOV CX, -5 ; in this case AL > -5
exit:
Conditional Jump Instruction

JL: Jump if first operand is Less then
second operand (as set by CMP
instruction). Signed.

if SF <> OF then jump

Syntax: [label:] JL
short-address
Example
MOV AL, -2
CMP AL, 5
JL label1
JMP exit
label1: MOV CX, 5 ; in this case AL < 5
exit: …
Practice

Write a program to compute sum of even
integers from 1 to 100 using LOOP
Conditional Jump instructions
JB/JNAE
[label:] JB/JNAE short-address
Jump Above/Equal or Jump Not
Above/Equal
Flag: ZF
Conditional Jump instructions
JBE/JNA
[label:] JBE/JNA short-address
Jump Below/Equal or Jump Not Above
Flag: AF, ZF
Special Arithmetic Test
JCXZ: Jump if CX is zero
 JC: Jump if carry
 JNC: Jump if no carry
 JO: Jump if overflow
 JNP: Jump if no overflow

Practice

Write a program that adds each value
defined in BYTE_TBL and store the sum in
BYTE_TOTAL
BYTE_TBL
BYTETOTAL
DB 0,5,6,4,9,7
DB 0
Assembling, Linking and
Executing Programs
Assembling: translate sourse program
(written in assembly language) into
machine code (object code)
Linking: complete machine code for the
object program, generate an executable
module
Assembling, Linking and
Executing Programs
Create *.asm
Editor
Assembler
Assemble *.asm
And create *.obj
Linker
Link
And create *.exe
Assembling a Source Program

Converts your source code into machine
code and displays any errors.
Assembling
*.asm
*.obj, *.lst, *.crf
Example
; Add two numbers and store the results into the third variable
page 60,132
TITLE
A04ASM1 (EXE) Move and add operations
; --------------------------------------------STACK
SEGMENT PARA STACK 'Stack'
DW
32 DUP(0)
STACK
ENDS
; ---------------------------------------------DATASEG SEGMENT PARA 'Data'
FLDD
DW
215
FLDE
DW
125
FLDF
DW
?
DATASEG ENDS
; ----------------------------------------------CODESEG SEGMENT PARA 'Code'
MAIN
PROC FAR
ASSUME SS:STACK,DS:DATASEG,CS:CODESEG
MOV AX,DATASEG
;Set address of data
MOV DS,AX
; segment in DS
MOV
AX,FLDD
;Move 0215 to AX
ADD
AX,FLDE
;Add 0125 to AX
MOV
FLDF,AX
;Store sum in FLDF
MOV
AX,4C00H
;End processing
INT
21H
MAIN
ENDP
;End of procedure
CODESEG ENDS
;End of segment
END
MAIN
;End of program
Example
===================================================================================================
[LINE]
LOC: MACHINE CODE
SOURCE
===================================================================================================
[
[
[
[
[
1]
2]
3]
4]
5]
:
:
:
:
:
[ 6]
; Add two numbers and store the results into the third variable
page 60,132
TITLE
A04ASM1 (EXE) Move and add operations
; --------------------------------------------STACK
SEGMENT PARA STACK 'Stack'
0000: 00 00 00 00 00 00 00 00 00 00 00 00 DW 32 DUP(0)
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00
[ 7]
:
STACK
ENDS
[ 8]
:
; ---------------------------------------------===================================================================================================
Example
===================================================================================================
[LINE]
LOC: MACHINE CODE
SOURCE
===================================================================================================
[ 9]
:
[ 10] 0040: D7 00
[ 11] 0042: 7D 00
[ 12] 0044: 00 00
[ 13]
:
[ 14]
:
------------
DATASEG
FLDD
FLDE
FLDF
SEGMENT PARA 'Data'
DW
DW
DW
215
125
?
DATASEG
ENDS
; -----------------------------------
Example
===================================================================================================
[LINE] LOC: MACHINE CODE
[ 16] 0050:
MAIN
FAR
===================================================================================================
[ 17]
:
SOURCE
PROC
ASSUME SS:STACK,DS:DATASEG,CS:CODESEG
[ 18] 0051: B8 04 00
MOV
AX,DATASEG
[ 19] 0054: 8E D8
[ 20] 0056: A1 00 00
MOV
MOV
DS,AX
AX,FLDD
[ 21] 0059: 03 06 02 00
ADD
AX,FLDE
[ 22] 005D: A3 04 00
Linking an Object Program
Combines more than one assembled
module into one executable program
 Generates an EXE module and initializes it
with special instructions to facilitate its
subsequent loading for execution

Linking an Object Program

*.map
START STOP LENGTH NAME CLASS
00000H 0003FH 0040H STACK STACK
00040H 00045H 0006H DATASEG DATA
00050H 00063H 0014H CODESEGCODE
Program entry at 0005:0000
Procedures

Procedure is a part of code that can be called from your
program in order to make some specific task.
makes program more structural and easier to
understand.
returns to the same point from where it was called.
Syntax:
name PROC
; the code of the procedure ...
RET
name ENDP
Procedures
CALL instruction is used to call a
procedure
 CALL is used to transfer controls
 RET is used to end execution of
procedure

Syntax:[label:] CALL procedure
[label:] RET [immediate]
Example
m1
m1
m2
m2
CALL m1
MOV AX, 2
RET ; return to operating system.
PROC
MOV BX, 5
CALL m2
RET ; return to caller.
ENDP
PROC
MOV CX, 10
RET; return to caller
ENDP
Procedure
NEAR: intra-segment procedure
 FAR PROC: inter-segment procedure

Program execution and Stack
CALL and PUSH store one word address
or value onto stack
 RET and POP pop and stack and access
the previously pushed word

Example
Example
Practice exercise
Code a procedure using LOOP that
calculate Fibonaci series:
1,1,2,3,5,8,13..
Limits to 7 loops
Each number is the sum of the preceding
two numbers
AX should store the current Fibonaci
number
Call this procedure from the main program

Practice exercise

Basic coding in assembly language