Page 14 - DCAP102_DCAP_401_Foundations of Computer Programming

Unit 1: Foundation of Programming Languages

1.5 Assembly Program and its Components Notes

Sample Program:

In this program we just display:
Line Numbers Offset Source Code
0001 DATA SEGMENT
0002 0000 MESSAGE DB “HAVE A NICE DAY!$”

0003 DATA ENDS
0004 STACK SEGMENT
0005 STACK 0400H
0006 STACK ENDS
0007 CODE SEGMENT

0008 ASSUME CS: CODE, DS: DATA SS: STACK
0009 Offset Machine Code
0010 0000 B8XXXX MOV AX, DATA
0011 0003 8ED8 MOV DS, AX

0012 0005 BAXXXX MOV DX, OFFSET MESSAGE
0013 0008 B409 MOV AH, 09H
0014 000A CD21 INT 21H
0015 000C B8004C MOV AX, 4C00H
0016 000F CD21 INT 21H
0017 CODE ENDS

0018 END
The details of this program are:

The Program Annotation

The program annotation consists of three columns of data: line numbers, offset and machine
code.

1. The assembler assigns line numbers to the statements in the source file sequentially. If the
assembler issues an error message; the message will contain a reference to one of these line
numbers.
2. The second column from the left contains offsets. Each offset indicates the address of an
instruction or a datum as an offset from the base of its logical segment, e.g., the statement
at line 0010 produces machine language at offset 0000H of the CODE SEGMENT and the
statement at line number 0002 produces machine language at offset 0000H of the DATA
SEGMENT.
3. The third column in the annotation displays the machine language produce by code
instruction in the program.

Segment numbers: There is a good reason for not leaving the determination of segment numbers
up to the assembler. It allows programs written in 8086 assembly language to be almost entirely

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