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Back to Assembly lang

Back to Assembly lang. name operation operand(s) ;comment. START: MOV CX , 5 ; যা ইচ্ছা লিখ! ‘ ; ’ দিও!. name operation operand(s) ;comment. Okay  letters, digits, ?, ., @, _, $, % Illegal names – If any blanks – aaa aaa If begin with a digit – 2asad

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Back to Assembly lang

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  1. Back to Assembly lang

  2. name operation operand(s) ;comment START: MOVCX, 5 ;যা ইচ্ছা লিখ! ‘;’ দিও!

  3. name operation operand(s) ;comment • Okay  letters, digits, ?, ., @, _, $, % • Illegalnames – • If any blanks – aaaaaa • If begin with a digit – 2asad • If ‘.’ not first char. – aq.12 • If has illegal char – aa&bb

  4. name operation operand(s) ;comment • For an Instruction: Symbolic operation code [opcode]: Assembler translates these codes into Machine lang opcode.  MOV, ADD, SUB, … • For an Directive: pseudo-operation code – pseudo-op, do not translate  PROC is used to create a procedure

  5. name operation operand(s) ;comment • An instruction may have 0/1/2 operands e.g., NOP ; no operands – does nothing INC AX ; 1 op. – adds 1 to contents of AX ADDdestination, source

  6. 4.2 Program data • Binary – 1011b, 1100B • Decimal – 10111, 10111d, -3419D 1,23 – x • Hex – start with a decimal digit, ends with ‘H’ – 3BA3H, 0FFFFH • Characters – within ‘aa’ or “aa”

  7. Pseudo-ops • DB – define data BYTE • DW – word • DD – doubleword – two consecutive words • DQ – quadword – 4 … • DT – tenbytes – 10…

  8. 4.3 Variables name operation operand(s) ;comment name DB initial value ; -128 ~ 127; or 0-255 e.g., ALPHA DB 4 ; variable ALPHA=4 AA DB ? ; uninitialized byte

  9. 4.3.3 Array EktaArray DB 10H, 20H, 22H Symbol Address Contents EktaArray 200h 10H EktaArray+1 201h 20H EktaArray+2 202h 22H

  10. For DW – 2 bytes Symbol Address Contents EktaArray 200h 10H EktaArray+2 202h 20H EktaArray+4 204h 22H

  11. WORD1 DW 1234H ; low Byte of WORD1 contains 34H ; high Byte of WORD1 contains 12H

  12. 4.5 basic instructions • MOV – move; contents of destination is replaced by the contents of source • XCHG – exchange; swapping Q: exa??

  13. ADD W1, AX ;W1 = W1 + AX ;W1 – changes with added/sum value ;AX – unchanged • SUB AX, DX ;Subtract DX from AX ;New value in AX – AX changes ; DX unchanged

  14. Direct ADD/SUB between memory locations WRONG! • ADD W1, W2 ; wrong as direct memory location Source Destination General Reg. Memory loc. Gen Reg. Yes Yes Memory Loc. Yes NO Constant Yes Yes

  15. INCIncrement • INC destination INC W1 ;e.g., W1=0003 Before W1=0003 After INC, W1=???? 0004

  16. DECDecrement • DEC destination DEC W1 ;e.g., W1=FFFF Before W1=FFFF After INC, W1=???? FFFE

  17. NEGnegate the contents of destination • NEG destination ; reg. / mem. ; replace the contents by it’s two’s complement NEG W1 ;e.g., W1=0002 Before W1=0002 After NEG, W1=???? FFFE

  18. Note: • Both types MUST be the same type e.g., MOV AH, ‘A’ ; what is in AH? ; ‘A’ = 41H MOV AX, ‘A’ ; what is in AX? 41H 0041H

  19. Do!High- to Assembly • B = A • A = 5 – A • A = B – 2 x A

  20. 1. B = A • MOV AX, A • MOV B, AX • A direct mem-to-mem move is illegal

  21. 2. A = 5 - A • MOV AX, 5 • SUB AX, A • MOV A, AX • NEG A • ADD A, 5

  22. 3. A = B – 2xA • MOV AX, B ;AX = B • SUB AX, A ;AX=B-A • SUB AX, A ;AX=B-A – A ; AX = B – 2A • MOV A, AX ; A = AX = B – 2A

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