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Memory Address

Memory Address. Segment-offset address Base location (segment) + logical location (offset) Example: For 32-bits segment-offset address, 08F1:0100 represents a 20-bits absolute address 09010 0 8 F 1 (0) 0000 1000 1111 0001 0000

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Memory Address

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  1. Memory Address • Segment-offset address • Base location (segment) + logical location (offset) • Example: • For 32-bits segment-offset address, 08F1:0100 represents a 20-bits absolute address 09010 • 0 8 F 1 (0) • 0000 1000 1111 0001 0000 • + 0 1 0 0 • 0 9 0 1 0

  2. Floating-Point Unit 80-bit Registers 48-bit Pointer Register ST(0) FPU Instruction Pointer ST(1) FPU Data Pointer Tag Register Control Register Status Register 16-bit Control Register ST(7) Opcode Register

  3. DUP Operator • db 20 dup(0) ; 20 bytes, all equal to zero • db 20 dup (?) ; 20 un-initialized bytes • db 4 dup(“ABC”) ; 12 bytes: “ABCABCABCABC” • db 4096 dup(0);

  4. Assembly Language • Basic elements • 1. Constant and expression • 3 • 3.5 • - 3.5 • 26. E+07

  5. Integer Constants • 26 decimal • 1Ah hexadecimal • 1101b binary • 36q octal • 2BH hexadecimal • 43Q octal • 36D decimal • 48d decimal

  6. Constant Expression, Symbolic constants and Character or String Constants • Constant expression • 5 26.5 4*20 -3*4/6 -2.301E+04 • A symbolic constant • rows = 5 columns = 10 • Number = rows * columns • Character or string constant • ‘ABC’ ‘X’ “ This is a test” “The dog is black”

  7. Assembly Language Statement • Consists of : • 1. A name, an instruction mnemonic, operands, and a comment. It has the following form: • [name] [mnemonic] [operands] [;comment] • Example: • call sub1 ; transfer of control

  8. Names • A name identifies a label, variable, symbolic, or a keyword. • What can be used as a name: • 1. A… Z a… z • 2. 0-9 • 3. ? • 4. _ Underscore • 5. @ • 6. $ • Length limit----maximum of 247 characters (in MASM)

  9. Variables and Labels • 1. A variable is a location in a program’s data area that has been assigned a name. • Such as: count1 db 50 ; • message db “ Hello world!”, odh, 0ah • 2. Label. If a name appears in the code area of a program, it is called a label. • Example: • LabelA: mov ax, 0 • mov bx, ffh

  10. Hello World Program • title Hello World Program (hello.asm) • ; This program displays "Hello, world!" • .model small • .stack 100h • .data • message db "Hello, world!",0dh,0ah,'$' • .code • main proc • mov ax,@data • mov ds,ax • mov ah,9 • mov dx,offset message • int 21h • mov ax,4C00h • int 21h • main endp • end main

  11. Analyze the Program • .model small ----specify the program’s memory model • For that model we can have: • Tiny--- code + data less than 64k • Samll--- code <=64k, data ,<=64k One code segment and one data segment • Medium---Data <=64k, code any size. Multiple code segment, one data segment • Compact---Code <= 64k, data any size. Multiple data segment, one code segment • Large---Code >64k, data >64k both multiple segment • Huge---Same as the large model, except that individual variables such as arrays may be large than 64k • Flat--- No segments. 32-bits addresses are used for both code and data. ***Protected mode only

  12. Standard Assembler Directives • end---end of program assembly • endp--- end of procedure • page---Set a page format for the listing file • proc---Begin procedure • title---Title of the listing file • .code--- Mark the beginning of the code segment • .data--- • .model--- • .stack---Set the size of the stack segment

  13. Data Allocation Directives • DB--------------------1 byte • DW-------------------2 • DD--------------------4 • DF, DP---------------6---define far pointer • DQ--------------------8 define Quadword • DT--------------------10 define 10 bytes

  14. Examples • Char1 db ‘A’ ; ASCII char. • Char2 db “A’ –10 ; expression • Smallest db –128 • Max_unsign db 255 • Myval db ? Only reserve memory, no initializeers • List db 10,20,30,40,50

  15. Characters and Integers are one and the same • Char db ‘A’ • Hex db 41h • Dec db 65 • Bin db 01000001 • Oct db 101q

  16. Type mix is allowed • List db 10, 20, 41h, 10011000b • List2 db 0ah, 29h, ‘a’, 22

  17. Strings • Cstring db “Good morning”,0 • Pstring db 12, “Good morning” • Longstring db “This is a long string, that” • db “ clearly is going to take” • db “ several lines to store”,0

  18. Symbolic Constants • Equate directives • They allow constants and literals to be given symbolic names. • 1. Equal-Sign Directive (redefinable) • The syntax is: name = expression • Examples: string = ‘XY’ • count = 500 • minInt = 8000h

  19. To assign a 32 bits integer---.386 is required • .386 • maxLong = 7FFFFFFFh ; maximum 32-bit signed value • minLong = 80000000h ; Minimum 32-bit signed value • “=“ defined symbols can be redefined any number of times.

  20. Example of Using Directives • count =5 • mov al , count • mov dl , al • count =10 • mov cx , count • count = 2000 • mov ax, count

  21. EQU and TEXTEQU directives • EQU is not redefinable • TEXTEQU is redefinable • Examples: maxint equ 32767; Numeric • float1 equ <3.1416> ; String • TEXTEQU syntax: • name TEXREQU <text> • name TEXTEQU textmacro

  22. Intel chip Instructions • 1. MOV---Data transfer instruction • Instruction format: • MOV reg, reg MOV reg, immed • MOV mem, reg MOV mem, immed • MOV reg, mem MOV mem16, segreg • MOV reg16, segreg • MOV segreg, immed16 • MOV segreg, reg16 • *** Flag bits are not affected by MOV instruction

  23. Examples • .data • count db 10 • total dw 4126h • bigVal dd 12345678h • .code • mov al, bl • mov bl, count • mov count, 26 • mov bl, 1

  24. Examples—cont… • mov dx, cx • mov bx, 8FE2h • mov total, 1000h • mov eax, ebx • mov edx, bigVal ; 32-bit memory to reg • ***Pay attention the the fact that operands size must match. Otherwise, the assembler will return an error for any size mismatch.

  25. Example • .data • count dw 20h ; 20h---here really mean 0020h • .code • mov al, count; error:

  26. XCHG Instruction • XCHG reg, reg • xchg ax, bx • xchg eax, ebx • XCHG reg, mem • xchg ax, value1 • XCHG mem, reg • xchg value2, cx

  27. Program example • Title Exchange Two Variables (Exchange.asm) • .model small • .stack 100h • .data • Value1 db 0ah • Value2 db 14h • .code • Main proc • Mov ax, @data ; initialize DS register • Mov ds, ax • Mov al, value1 • Xchg value2, al • Mov value1, al • Mov ax, 4c00h • Int 21h • Main endp • End main; Question: Why don’t we use xchg value1, value2?

  28. Arithmetic Instructions • ADD and SUB instructions • ADD reg, reg • ADD mem, reg • ADD reg, mem • ADD reg, immed • ADD mem, immed • ADD accum, immed • Flag O D I S Z A P C • SUB has the similar instruction format * * * * * *

  29. Examples • Mov ax, 10 • Sub ax, 10 ; AX=0, ZF =1 • Mov bx, 1 • Sub bx, 2 ; BC = FFFF, SF = 1 • Mov ax, 0FFh • Add al, 1 ; AL = 00 , CF = 1

  30. Basic Operand Types • There are three basic types of operands: • 1. Immediate----a constant • 2. Register-------one of the CPU’s register • 3. Memory---a reference to a mem.Location • There are six different types of memory operands: • Direct, direct-offset, register-indirect • Indexed, base-indexed, and base-indexed with displacement

  31. Example • mov ax, [si] --- this is called register-indirect • Here si register hold the beginning address for a list of numbers. • The first number in the address will be moved to al and the second number will be moved into ah.

  32. Immediate operands, Direct Operands, and Direct-Offset operands • 1. Immediate operands: • Mov al, 10 ; ----a number • Mov eax, 12345678h ; ---a 4-byte number • Mov dl, ‘X’ ; --- a character • Mov ax, (40 *50) ; arithmetic expression

  33. Direct Operands • .data • Count db 20 • Wordlist dw 1000h, 2000h • LongVal dd 11223344h • .code • Mov al, Count • Mov bx, Wordlist +2 • Mov edx, LongVal

  34. Direct Offset Operands • .data • Array db 0ah, 0bh, 0ch, 0dh • .code • Mov al, array ; 0ah-al • Mov bl, array +1 ; 0bh  bl • Mov cl, array + 2 ; 0ch  cl • Mov dl, array +3 ; 0dh  dl

  35. Another Example

  36. IA – 32 Processor Architecture • IA – 32 processor have three basic mode of operations: • 1. Protected Mode • 2. Real-address Mode • 3. System Management Mode

  37. Protected Mode • IA-32 processors have three basic modes of operation: Protected mode, Real-address mode and System Management mode. In addition, the Virtual-8086 mode is a special case of Protected mode.

  38. 1. Protected Mode • Protected mode is the native state of the processor, in which all instructions and features are available. • Programs are given separate memory areas (called segment), and the processor detects any attempt by a program to reference memory outside its assigned segment. • Each program can address up to 4GB memory.

  39. Virtual – 8086 Mode • While in Protected mode, the processor can directly execute Real-address mode software such as MS-DOS programs in a safe multitasking environment. • In other word, even is an MS-DOS program crashes, it will not affect other program running at the same time.

  40. Real-address mode • It offers us a few more features, such as the ability to switch into other two modes. • Only 1 MB of memory can be addressed: • 00000h-FFFFFh • The processor can only run one program a time.

  41. System Management Mode • SSM-mode • It provides an operating system with a mechanism for implementing such functions as power management and system security. • These functions are usually implemented by computer manufacturers who want to customize the processor for a particular system setup.

  42. Homework11 • Write and run an assembly program under debug that will: • 1) Add numbers from 1 to 1000. • Note: you would need these following instructions: • A) jz – jump if zero • B) mov cx, number of times (1000 in Hex.) • C) create the labels that tells where to go.

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