lect2-assemb1

8/8/2019 lect2-assemb1

1/16

10/23/2010CAP2211

Lecture 2

BASIC INSTRUCTIONS


2/16

10/23/2010CAP2212

MOV instruction

Is used to transfer data :

between registers,

between a register & a memory location.

Or To move a number directly into a register or

memory location.

Syntax

MOV destination , source


3/16

10/23/2010CAP2213

Examples:

MOV AX , WORD1

MOV AX , BX

MOV AH , A


4/16

10/23/2010CAP2214

XCHG instruction

(Exchange) operation is used to exchange

the contents of

two registers, or

a register and a memory location

SyntaxXCHG destination , source


5/16

10/23/2010CAP2215

Examples:

XCHG AH , BL

XCHG AX , WORD1


6/16

10/23/2010CAP2216

Restrictions on MOV & XCHG

SourceOperand

GeneralRegister

SegmentRegister

MemoryLocation

Constant

GeneralRegister

yes yes yes noSegmentRegister yes no yes no

MemoryLocation yes yes no no

Constant yes no yes no

MOV Destination Operand


7/16

10/23/2010CAP2217

Restrictions on MOV & XCHG

XCHG Destination Operand

SourceOperand

GeneralRegister

MemoryLocation

General

Register yes yes

MemoryLocation yes no


8/16

10/23/2010CAP2218

ADD & SUB

Are used to add & subtract the contents of

two registers,

a register & memory location , or

add ( subtract ) a number to ( from ) a register or amemory location.

Syntax

ADD destination , source

SUB destination , source


9/16

10/23/2010CAP2219

Example

Examples

ADD WORD1 , AX

SUB AX , DX

ADD BL , 5


10/16

10/23/2010CAP22110

Legal combinations of operands forADD & SUB

Memory locationGeneral RegisterSource Operand

yesyesGeneral Register

noyesMemory location

yesyesConstant

Destination operand


11/16

10/23/2010CAP22111

INC ( increment )&DEC ( decrement )

INC: Is used to add 1 to the contents ofa

Register or

Memory location

DEC: Is used to subtract 1 from thecontents of a

Register or

Memory location


12/16

10/23/2010CAP22112

SyntaxINC destination

DEC destination

Examples:

INC WORD1

DEC BYTE1


13/16

10/23/2010CAP22113

NEG

Is used to negate the contents of the destination.

The destination may be aregisterormemory location.

It does this by replacing the contents by itstwos complement.

SyntaxNEG destination


14/16

10/23/2010CAP22114

Translation of HLL toAssembly Language

Statement Translation

A = 5 A MOV AX , 5 ; put 5 in AX

SUB AX , A ; AX. 5 AMOV A , AX ; put it in A

There is another shorter way :


15/16

10/23/2010CAP22115

NEG A ; A = - A

ADD A , 5 ; A = 5 - A


16/16

10/23/2010CAP22116

Translation of HLL toAssembly Language

Statement Translation

A = B 2 * A MOV AX , B ; AX has B

SUB AX , A ; AX has B ASUB AX , A ; AX has B 2 * A

MOV A , AX ; move results to B

Documents

lect2-assemb1