8088/8086 Instruction I

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Direction Flag Direction Flag (DF) is used to control the way SI and DI are adjusted during theexecution of a string instruction— DF=0, SI and DI will auto-increment during the execution; otherwise, SI and DIauto-decrement— Instruction to set DF: STD; Instruction to clear DF: CLD— Example:CLDMOV CX, 5REP MOVSBAt the beginning of execution,DS=0510H and SI=0000HDS : SI0510:00000510:00010510:00020510:00030510:00040510:00050510:000653484F50504552SHOPPERSI CX=5SI CX=4SI CX=3SI CX=2SI CX=1SI CX=0Source String8-14
String Instructions MOVSB (MOVSW)— Move byte (word) at memory location DS:SI to memory location ES:DI andupdate SI and DI according to DF and the width of the data being transferred— It does not modify flags—Example:MOV AX, 0510HMOV DS, AXMOV SI, 0MOV AX, 0300HMOV ES, AXMOV DI, 100HCLDMOV CX, 5REP MOVSBDS : SI0510:00000510:00010510:00020510:00030510:00040510:00050510:000653484F50504552Source StringSHOPPERES : DI0300:0100Destination String8-15
Page 1 and 2: ECE 424 Design of Microprocessor-Ba
Page 3 and 4: Addressing ModesAddressing Modes Im
Page 5 and 6: Flags Commonly Tested During the Ex
Page 7 and 8: What is a Stack ?Instructions for S
Page 9 and 10: Data Transfer Instructions SAHF—
Page 11 and 12: String Instructions String is a col
Page 13: REPZ String InstructionRepeat Prefi
Page 17: String Instructions SCASB (SCASW)

8088/8086 Instruction I

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