32-bit instruction mode(80386-Pentium 4 only) Machine Language 16-bit instruction mode Opcode 1-2 bytes MOD-REG-R/M 0-1 bytes Displacement 0-1 bytes Immediate 0-2 bytes 32-bit instruction mode(80386-Pentium 4 only) Address size 0-1 bytes Register size 0-1 bytes Opcode 1-2 bytes MOD-REG-R/M 0-1 bytes Scaled-index 0-1 bytes Displacement 0-4 bytes Immediate 0-4 bytes

The Opcode D W Opcode D=1 data flow to register field from R/M field. D=0 data flow to the R/M field from register field. W=1 data size is a word or doubleword. W=0 data size is a byte.

Example: Suppose that a two-byte instruction MOD REG R/M MOD Function 00 No displacement 01 8-bit sign-extended displacement 10 16-bit signed displacement 11 R/M is a register For MOD=11:- Code W=0 W=1(word) w=1(DW) 000 AL AX EAX 001 CL CX ECX 010 DL DX EDX 011 BL BX EBX 100 AH SP ESP 101 CH BP EBP 110 DH SI ESI 111 BH DI EDI Example: Suppose that a two-byte instruction 8BECH 1 Opcode D W MOD REG R/M

Example: Suppose that a two-byte For MOD= 00, 01, 10:- R/M Code Addressing Mode 000 DS:[BX+SI] 001 DS:[BX+DI] 010 SS:[BP+SI] 011 SS:[BP+DI] 100 DS:[SI] 101 DS:[DI] 110 SS:[BP]* 111 DS:[BX] Example: Suppose that a two-byte Instruction 8A15H 1 Opcode D W MOD REG R/M

Movement Instructions PUSH/POP LEA : load a 16- or 32- bit register with the offset address of the data specified by the operand. LEA AX,NUMB LEA EAX,NUMB LDS, LES, LFS, LGS, and LSS : load any 16- or 32-bit register with an offset address and the DS, ES, FS, GS, or SS segment register with a segment address. LDS BX,[DI] LDS EBX,[DI]

STRING DATA TRANSFER LODS : loads AL, AX, or EAX with data stored at the data segment, offset address indexed by the SI register. LODSB AL=DS:[SI]; SI=SI±1 STOS :stores AL, AX, or EAX at the extra segment memory location addressed by the DI register. STOSB ES:[DI]=AL: DI=DI±1 The repeat prefix : is add to any string data transfer instruction except the LODS. REP STOSW ES:[DI]=AX: DI=DI±2, CX=CX-1

MOVS : it transfers data from one memory location to another (8086-p4). Transfers a B, W, or D from data segment location addressed by SI to extra segment location addressed by DI. MOVSB ES:[DI]=DS:[SI]; DI=DI±1, SI=SI±1 4. INS : (not available on the 8086/8088) transfer a B, W, or D of data from I/O device into the extra segment memory location addressed by the DI register. Note that the I/O address is contained in the DX register. INSD ES:[DI]=[DX]; DI=DI±4 5. OUTS : (not available on the 8086/8088) transfer a B, W, or D of data from the data segment location addressed by SI to an I/O device. OUTSW [DX]=DS:[SI]; SI=SI±2

MISCELLANEOUS DATA TRANSFER Instructions 1. XCHG: exchanges the contents of a register with the contents of any other register or memory location. XCHG AX,CX exchanges the contents of AX with CX Byte, word, or doubleword – size. Use any addressing mode except immediate addressing. Segment registers. Memory to memory. LAHF: transfers the rightmost eight bits of the flag register into the AH register. SAHF : transfers the AH register to the rightmost eight bits of the flag register.

XLAT: converts the contents of the AL register into a number stored in a memory table. 5. IN and OUT: the content of AL, AX, or EAX are transferred only between the I/O device and the µP. IN: transfers data from an external I/O device into AL, AX, or EAX. OUT: transfers data from AL, AX, or EAX to an external I/O device. IN AX,p8 IN AL,DX OUT p8,AL OUT DX,EAX

MOVSX: (move and sign – extend) convert 8- or 16-bits signed numbers into 16- or 32-bit signed number (80386-P4). MOVSX CX,BL BL=84H, CX=FF84H MOVZX: (move and zero – extend) convert unsigned 8- or 16-bits numbers into unsigned 16- or 32-bit number (80386-P4). MOVZX DX,AL AL=34H, DX=0034H 8. BSWAP EAX EAX=55667788H EAX=88776655H CMOV:( conditional move) is new to the Pentium-Pro- P4. CMOVC move if carry