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Comunicación y Gerencia. Fundamentals of Assembly Language. Click to add Title. Click to add Text. Click To add Subtitle. Lesson plan. Review of existing concepts Data transfer instructions Practice Basic arithmetic instructions and Repetitive move operations Practice.

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  1. Comunicación y Gerencia Fundamentals of Assembly Language Click to add Title Click to add Text Click To add Subtitle

  2. Lesson plan • Review of existing concepts • Data transfer instructions • Practice • Basic arithmetic instructions and Repetitive move operations • Practice

  3. Review of existing concepts • Comments • Directives (page, segment, title) • Data type (Byte (DB), Word(DW), Doubleword(DD), String • Some arithmetic operations: ADD,SUB,MUL,DIV

  4. Data transfer instructions • MOV instruction • Transfers data referenced by the address of the second operand to the address of the first operand • Destination has to have the same length as source [label:] MOV register/memory register/memory/immediate Example: MOV F, AX ; // Move content of AX to the variable F MOV CX, D ;// Move value of D to CX MOV ES, AX MOV AX, 215

  5. Note • MOV instruction can’t: • set the value of the CS and IP registers. • copy value of one segment register to another segment register (should copy to general register first). MOV ES, DS • copy immediate value to segment register (should copy to general register first). MOV DS, 100 • MOV instruction can’t: • set the value of the CS and IP registers. • copy value of one segment register to another segment register (should copy to general register first). MOV ES, DS • copy immediate value to segment register (should copy to general register first). MOV DS, 100

  6. MOVSB and MOVSW • MOVSB: Copy byte at DS:[SI] to ES:[DI]. Update SI and DI.Algorithm: ES:[DI] = DS:[SI] if DF = 0 then SI = SI + 1 DI = DI + 1 else SI = SI - 1 DI = DI - 1 DF: direction flag from the flag register

  7. MOVSB and MOVSW • MOVSW: Copy word at DS:[SI] to ES:[DI]. Update SI and DI. ES:[DI] = DS:[SI] if DF = 0 then SI = SI + 2 DI = DI + 2 else SI = SI - 2 DI = DI - 2 DF: direction flag from the flag register

  8. XCHG instruction • XCHG swap the two data items [label:] XCHG register/memory, register/memory Example: MOV AL, 5 MOV AH, 2 XCHG AL, AH ; AL = 2, AH = 5 XCHG AL, AH ; AL = 5, AH = 2

  9. LEA instruction • Load Effective Address. REG = address of memory (offset) [label:] LEA register/memory Example: LEA AX, m ;load offset address of m to AX

  10. Arithmetic instructions • INC and DEC instruction • Increasing or decreasing the contents of register or memory location by 1 [label:] INC/DEC register/memory Flag: OF, SF and ZF OF:is set when an instruction resulted in a carry into the sign bit of the result. SF: is set if the sign bit of a result is set ZF: is set if the result is equal to 0.

  11. Arithmetic instructions • ADD [label:] ADD/SUB operand1, operand 2 operand1 =operand 1 + operand 2 Operand 1: register/memory Operand 2: register/memory/immediate

  12. Arithmetic instructions • SUB [label:] SUB operand1, operand 2 operand1 =operand 1 - operand 2 operand 1: register/memory operand 2: register/memory/immediate

  13. Arithmetic instructions • MUL operand Unsigned multiply. Operand: register/memory

  14. Arithmetic instructions • IMUL operand Signed multiply. Operand: register/memory Example: MOV AX, -2 MOV CX, -3 IMUL CX ; AX = +6 CF = 0

  15. Arithmetic instructions • DIV operand Unsigned multiply. Operand: register/memory when operand is a byte:AL = AX / operandAH = remainder (modulus) when operand is a word:DX = remainder (modulus)

  16. Arithmetic instructions • IDIV operand Signed multiply. Operand: register/memory when operand is a byte:AL = AX / operandAH = remainder (modulus) when operand is a word:DX = remainder (modulus)

  17. Practice Write a program to convert from Celsius to Fahrenheit and vice versa: Tc = (5/9)*(Tf-32) Tc: censius Tf: fahrenheit (The result may not be accurate due to the integer division but that is fine)

  18. Repetitive move instructions TITLE A04ASM1 (EXE) Move and add operations ; --------------------------------------------- STACK SEGMENT PARA STACK 'Stack' DW 32 DUP(0) STACK ENDS ; ---------------------------------------------- DATASEG SEGMENT PARA 'Data' STRING1 DB "12345678","$" STRING2 DB ? DATASEG ENDS

  19. Repetitive move instructions CODESEG SEGMENT PARA 'Code' MAIN PROC FAR MOV AX, dataseg MOV DS, AX MOV ES, AX MOV CX, 09 ; Initialize to move 9 characters LEA SI, STRING1 ; Initialize source index register to offset of string 1 LEA DI, STRING2 ; Initialize destination index register to offset of string 2 BEGINLOOP: MOV AL,[SI] ; Get a current character from string 1 to AL MOV [DI], AL ; Move it to the current character in string 2 INC SI ; Move to the next character in string 1 INC DI ; Move to the next character in string 2 DEC CX ; Decrease the count for loop JNZ BEGINLOOP ; Continue to loop if count is not 0 MOV AH, 09H LEA DX, STRING2 int 21H ; Display String 2 MAIN ENDP ;End of procedure CODESEG ENDS END MAIN ;End of program

  20. Result

  21. Repetitive move instructions • DEC CX ZF = 1 if CX = 0 • JNZ LABEL if ZF = 0 then jump to the label

  22. Practice • Develop an assembly program to: • Define byte items: BYTE1 and BYTE2 (Assign any values for these two variables) • Define a word item: WORD3 and WORD3=0 • Move content of Byte1 to AL • Add content of Byte2 to AL • Set DL= 42H • Exchange the content of AL and DL • Multiply the contents of AL by DL • Transfer product from AX to WORD3

  23. Addressing mode • Register addressing: E.g ADD AX, BX fastest type of operations • Immediate addressing Immediate contains a constant value or an expression E.g: MOV AX, 0245H • Direct memory addressing One of operand references a memory location and the other operand references a register E.G MOV FLDF, AX

  24. Addressing mode • Direct-Offset addressing use arithmetic instruction to modify an address e.g MOV CX, DATAZ+2 • Indirect memory addressing Use BX and BP, DI and SI within [ ] e.g. MOV [BX], CL

  25. Addressing mode Base Displacement Addressing Uses BX, BP and DI, SI and combine with a displacement to form an effective address E.g MOV AL,[SI+2] Base-Index Addressing Combine BX,BP with DI,SI to form effective address E.G MOV AL,[BX+SI]

  26. Addressing mode Base-Index Displacement Addressing Combine BX, BP and DI, SI and a displacement to form an effective address E.g MOV AL,[BX+SI+2]

  27. NEAR and FAR address NEAR address consists of 16 bit offset portion of an address used in real mode FAR address consists of both the segment and offset portions in the form of 32 bit segment:offset

  28. SEGMENT OVERRIDE PREFIX Example: MOV ES:[SI+2], CL ; move CL to ES:[SI+2]

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