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MACROS

MASM

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MACROS

A macro is a group of instructions that perform

a task, just as procedure performs one task

All the instructions defined in the macro are

inserted in the program at the point of usage

Name of macro and any parameters associated

with it are typed , and the assembler then

inserts them into the program.

Macro is faster than procedure because no

CALL and RET

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MOVE MACRO A, B

PUSH AX

MOV AX, B

MOV A, AX

POP AX

ENDM

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MOV CX,100

MOVE VAR1, VAR2PUSH AXMOV AX, VAR2MOV VAR1, AXPOP AX

MOV BX,VAR1

MOVE VAR3, VAR4PUSH AXMOV AX, VAR4

MOV VAR3, AXPOP AX

MOV DX,VAR3ADD BX,DX

DEC CX

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SOFTWARE INTERRUPTS

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ApplicationPrograms

Command ProcessorCOMMAND.COM

MS-DOS KernelMSDOS.SYS

BIOSIO.SYS

SystemH/w

MS-DOS FUNCTIONS & BIOS CALLS

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BIOS Hardware Specific

Provided by manufacturer

Two parts

Resident (BIOS)

Non-Resident (IO.SYS)

Offers convenient way to add funcs toBIOS

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INT NNH

INT 21H - DOS INTERRUPT

INT 10H BIOS INTERRUPT

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INT

Operates similar to call

Processor first pushes the Flags

TF, IF cleared

Next the processor pushes the current CS contents on

to the stack

Next IP is pushed

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Sequence of events for INT 08H

CS:IP 0100:0200H

Flag - 0F81H

O D I T S Z A P C

004FH SP-1 0FH004EH SP-2 81H

004DH SP-3 01H004CH SP-4 00H004BH SP-5 02H

004AH SP-6 00H

SP Initial

0050H

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08 * 04 = 20H (32)

00020H IP

00022H CS

Memory/ISR table00020H 20H00021H 00H00022H 50H

00023H 08H

0850H:0020H

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IRET

Used at end of ISR

For stack handling

004FH SP-1 0FH004EH SP-2 81H004DH SP-3 01H

004CH SP-4 00H004BH SP-5 02H004AH SP-6 00H

Flag 0F81H

0100H

0200H

SP Final 0050H

SP Initial

004AH

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MISCELLANEOUS INSTRUCTIONS

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ADDITIONAL INSTRUCTIONS

SAHF- Store AH to Flag Register (Lower)

LAHF- Load Flag into AH Register (Lower)

CMC- Complement Carry Flag

STI

CLI XCHG DSR,SRC

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ADDITIONAL INSTRUCTIONS

MOVSX DST, SRC

MOVZX DST,SRC

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ADDITIONAL INSTRUCTIONS

SHLD DST, SRC, Count

SHRD DST, SRC, Count

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ADDITIONAL INSTRUCTIONS

BSWAP REG32

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ADDITIONAL INSTRUCTIONS

XADD

XADD REG1,REG2