EE180: Microprocessor Systems Lecture Notes 4

Data directives – db, dw, dd, dq, dt

Type of data items
a.    Constants
b.    Variables

“DUP” (duplicate) – used to define repeated values of a data item.
                       EX: hypens    db    35 DUP(“-“) ; repeat “-“ 35 times

Type of number	Allowed Range
Unsigned	0 to 255
Signed	-127 to 128

Types of Data
Building block	Size (In Bytes)	Uses
Byte	1	Hold small number
Word	2	Use to hold large number and addresses
Dword	4	Used for calculations and hold addresses
Qword	8	Used for calculations
tbyte	10

Attribute – describes a particular characteristics of a data item

Attributed of a Data Items
a.    Type – number of bytes reerved for each building block
b.    Length – total number of building blocks that make up the data item
c.    Size – total number of bytes reserved for the data item
d.    Seg – the address of the beginning of the segment in which data item lies
e.    Offset – the address of the first byte of the data item

Operator – symbol used at assembly time to affect the value of an operand

Operator	Meaning
+	Add
-	Subtract
*	Multiply
/	Divide
MOD	Modulo

EQU (equate) directive allows to define symbols that stand for specific values while your program is being assembled.

Share: