Introduction to Computer
Organization and Assembly
Language
Sheet 1
Program Comment
• A semicolon marks the beginning of this field, and
the assembler ignores anything typed after the
semicolon.
• Example:
• MOV CX, 0
; CX counts terms, initially 0
Identifiers
•
Can be from 1 to 31 characters long (not case sensitive).
•
May consist of letters, digits, and the special characters.
•
? . @ _ $ % (Thus, embedded blanks are not allowed).
•
Names may not begin with a digit.
•
If a dot is used, it must be the first character.
Defining Types of data
[name]
Dn
•Syntax:
name
Dn initial_value
expression
Defining Types of data Cont.
• Dn (Directive):
Pseudoop
DB
DW
DD
DQ
DT
Stands for
Define Byte
Define Word
Define Doubleword
Define Quadword
Define Tenbytes
Question 1
Q1: Tell whether each of the following identifiers is
Valid or Invalid.
Identifier
Valid \ Invalid
Valid \ Invalid
Identifier
Open_File Valid
Count
Valid
First.
Invalid: Dot is not the
first character.
@@myfile
Valid
2_main
Invalid: Begins with a
digit.
@my file
Invalid: Contains a
blank.
Question 2
Q2: Give data definition pseudo-ops to define each of
the following:
a) A word variable X initialized to 41.
X DW 41
Question 2 Cont.
Q2: Give data definition pseudo-ops to define each of
the following:
b) A word variable WORD1, uninitialized.
WORD1 DW ?
Question 2 Cont.
Q2: Give data definition pseudo-ops to define each of
the following:
c) A byte variable Y initialized to 32h.
Y DB 32H
Question 2 Cont.
Q2: Give data definition pseudo-ops to define each of
the following:
d) A byte variable ITEM containing the hex equivalent to decimal
71.
ITEM DB 47H
Question 2 Cont.
Q2: Give data definition pseudo-ops to define each of
the following:
e) A word array ARRAY1, initialized to the first 5 positive integers
(i.e. 1-5).
ARRAY1 DW 1,2,3,4,5
Question 2 Cont.
Q2: Give data definition pseudo-ops to define each of
the following:
f) A 30 bytes array ARR, with each entry initialized to 10H.
ARR DB 30 DUP (10H)
Question 2 Cont.
Q2: Give data definition pseudo-ops to define each of
the following:
g) A constant LENGTH with value 20, another constant WIDTH
with value 10, and constant AREA using LENGTH and WIDTH
that you just defined (Note: area = length * width).
LENGTH EQU 20
WIDTH EQU 10
AREA EQU length * width