Topics
¾
Addressing modes (cont.) Assembly programming A sample program Directives Simplified segment definition
¾ ¾
Control transfer instructions Instruction set of x86
¾
Executing assembly programs
¾ ¾
2102440 Introduction to Microprocessors
¾ ¾
Chapter 2 Assembly Programming
z
z
Directives
Unsigned addition and subtraction
Suree Pumrin, Pumrin, Ph.D. 1
Addressing Modes (cont.)
Examples of Addressing Modes (I)
It describes the types of operands and the way they are accessed from the CPU.
Register Immediate Direct Register indirect
1. 2. 3. 4.
¾ Direct
MOV AX, BX ADD AL, 10H MOV CX, [1200H] MOV AL, [BX]
z
5.
Based relative
MOV CX, [BX+10H]
6.
Indexed relative
MOV AX, [SI+15H]
MOV DL, [2400H] ; move contents of DS:2400H into DL
¾ Register indirect
SI,DI
z
MOV AL, [BX]
z
MOV [DI], AH
BP
DI
Based indexed relative
7.
MOV AH, [BX+DI+5H] BP
SI
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Examples of Addressing Modes (II) ¾
2
2102440 Introduction to Microprocessors
; move the contents of the memory location DS:BX into AL ; move contents of AH into DS:DI 4
2102440 Introduction to Microprocessors
Offsets Registers for Various Segments
Based relative z
z
MOV CX, [BX] + 10H ; move DS:BX+10H and DS:BX + 10H + 1H into CX MOV AL, [BP] + 5H ; PA = SS:BP+5H
¾
Indexed relative
¾
Based indexed relative
z
z z
MOV DX, [SI] + 5H
Segment register
CS
Offset IP register(s) register(s)
DS
ES
SS
SI, DI, BX
SI, DI, BX
SP, BP
; PA = DS:SI+5H
MOV CL, [BX][DI]+8H MOV AH, [BP][DI]+12H
; PA = DS:BX+DI+8H ; PA = SS:BP+DI+12H
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1
Summary of 80x86 Addressing Modes
Segment Overrides Instruction
Segment Used
MOV AX, CS:[BP]
Addressing Mode
Operand
Default Segment
Register
Reg
none
Immediate
Data
none
Direct
[offset]
DS
Register indirect
[BX] [SI] [DI]
DS DS DS
Default Segment
CS:BP
SS:BP
MOV DX, SS:[SI]
SS:SI
DS:SI
MOV AX, DS:[BP]
DS:BP
SS:BP
MOV CX, ES:[BX]+12H
ES:BX+12H
DS:BX+12H
MOV SS:[BX][DI]+32H, AX
SS:BX+DI+32H
DS:BX+DI+32
2102440 Introduction to Microprocessors
Based relative
[BX]+disp [BP]+disp
DS SS
Indexed relative
[DI]+disp [SI]+disp
DS DS
Based indexed relative
[BX][SI]+disp [BX][DI]+disp [BP][SI]+disp [BP][DI]+disp
DS DS SS SS
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2102440 Introduction to Microprocessors
Assembly Instruction
Segments of a Program
label: mnemonic operands; comment
label Same
optional
¾ ¾ ¾
¾
optional
optional
label
Label cannot exceed 31 characters and must be unique. The mnemonic (instruction) and operands fields is used for the real tasks. PseudoPseudo-instructions called “directive” directive” give directions to the assembler on how it translate the instructions into machine code. Comment field begins with a “;”. 2102440 Introduction to Microprocessors
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Shell of an Assembly Program
label
SEGMENT [options] ;place the statements here ENDS
Example: STSEG SEGMENT DB 64 DUP(?) STSEG ENDS
;the segment directive ;reserves 64 bytes
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Simple Assembly Program
;THE FORM OF AN ASSEMBLY LANGUAGE PROGRAM STSEG SEGMENT DB 64 DUP(?) STSEG ENDS ;---------------------DTSEG SEGMENT ; ;place data here ; DTSEG ENDS ;---------------------CDSEG SEGMENT MAIN PROC FAR ;this is the program entry point ASSUME CS:CDSEG, DS:DTSEG, SS:STSEG MOV AX,DTSEG ;bring in the segment for data MOV DS,AX ;assign value to DS ; ;place code here ; MOV AH, 4CH ;return control to operating system INT 21H ;return to DOS MAIN ENDP CDSEG ENDS END MAIN ;this is the program exit point
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;THE FORM OF AN ASSEMBLY LANGUAGE PROGRAM STSEG SEGMENT DB 64 DUP(?) STSEG ENDS ;---------------------DTSEG SEGMENT DATA1 DB 52H DATA2 DB 29H SUM DB ? DTSEG ENDS ;---------------------CDSEG SEGMENT MAIN PROC FAR ;this is the program entry point ASSUME CS:CDSEG, DS:DTSEG, SS:STSEG MOV AX,DTSEG ;load the data segment address MOV DS,AX ;assign value to DS MOV AL,DATA1 ;get the first operand MOV BL,DATA2 ;get the second operand ADD AL,BL ;add the operands MOV SUM,AL ;store result in location SUM AH,4CH ;set up to MOV INT 21H ;return to DOS MAIN ENDP CDSEG ENDS END MAIN ;this is the program exit point
11
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2
Executable Program (I) EDITOR PROGRAM
Executable Program (II)
There are three steps to create an executable assembly language program.
myfile.asm
(1) Edit the program: ASSEMBLER PROGRAM
keyboard Æ myfile.asm (2) Assemble the program:
myfile.lst
myfile.crf
myfile.asm Æmyfile.obj
other files .obj
myfile.obj
(3) Link the program:
LINKER PROGRAM
myfile.obj Æ myfile.exe myfile.map
.asm: the source file .obj: the assembler converts the .asm file into machine code (object file). .lst: (optional) it lists all the opcodes and offset addresses as well as errors that the assembler detected. .crf: (optional) the cross-reference lists all the symbols and labels used in the program. .map: it gives the name of each segment, where it starts, where it stops, and its size in bytes. .exe: It can be executed by microprocessor. (ready-to-run version of a program)
myfile.exe 2102440 Introduction to Microprocessors
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2102440 Introduction to Microprocessors
DEBUG executable program
TASM style DOSSEG; "TASM style“ IDEAL MODEL SMALL SEGMENT DDD ;your data in Data Segment ENDS SEGMENT SSS ;your data in Stack ENDS SEGMENT CCC ASSUME CS:CCC, DS:DDD, SS:SSS MAIN: MOVE AX,DDD MOV DS,AX ;your Assembly code MOV AH, 4CH INT 21H ENDS END MAIN
> DEBUG myfile.exe -U CS:0 1 (unassemble) unassemble) 1064:0000 B86610 MOV AX, 1066 -D 1066:0 F (Dump memory) 1066:0000 52 29 …00 R)… 16
ตัว
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2102440 Introduction to Microprocessors
Data Directives ¾
ORG (origin)
¾
DB (define byte)
z
16
DUP ¾
Indicate the beginning of the offset address.
DUP (duplicate) Duplicate a given number of characters. ORG 0030H DATA7 DB 0FFH, 0FFH, 0FFH; Fill 3 bytes with FFH ORG 38H DATA8 DB 3 DUP (0FFH) ; Fill 3 bytes with FFH ORG 40H DATA9 DB 32 DUP (?) ; Set aside 32 bytes DATA10 DB 5 DUP (2 DUP (99H)); Fill 10 bytes with 99H z
Allocate memory in bytebyte-sized chunks ’ ’ indicates ASCII strings z DATA1 DB 25 ; Decimal DATA2 DB 10001001B ; Binary DATA3 DB 12H ; HEX ORG 0010H DATA4 DB ’2591’ ; ASCII Numbers 2591’ ORG 0018H DATA5 DB ? ; Set aside a byte ORG 0020H DATA6 DB ’Hello world’ ;ASCII Characters world’ z
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3
DW ¾
EQU, DD, DQ, and DT
DW (define word) z
¾
Allocate memory 2 bytes (one word) at a time.
DATA11 DATA12 DATA13 DATA14 DATA15
Define a constant without occupying a memory location. COUNT EQU 25H MOV CX, COUNT
z
ORG 70H DW 954 ; Decimal DW 100110101110B ; Binary DW 253FH ; HEX ORG 78H DW 9,2,7,0CH,00100001B,5,’ 9,2,7,0CH,00100001B,5,’HI’ HI’; Miscellaneous data DW 8 DUP(?) ; Set aside 8 words 2102440 Introduction to Microprocessors
EQU (equate)
¾
DD ( define doubleword) doubleword)
¾
DQ (define quadword) quadword)
¾
DT (define ten bytes)
z
z
z
Allocate 44-byte memory locations. Allocate 88-byte memory locations. It is used for memory allocation of packed BCD numbers.
19
Examples of DD, DQ, and DT
Memory Model
ORG 00A0H DATA16 DD 1023 ; Decimal DATA17 DD 10010010110011000110B ; Binary DATA18 DQ 5C348FH ; HEX DATA19 DT 123922910650; BCD (maximum of 10 bytes or 18 digits) DATA20 DT ? ; Nothing 2102440 Introduction to Microprocessors
Model
Max. Code (bytes)
Max. Data (bytes)
Small
64K
64K
Medium
> 64K
64K
Compact
64K
> 64K
Large
> 64K
> 64K
Tiny
Code + Data < 64K
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2102440 Introduction to Microprocessors
Shell of an Assembly Program (Simplified Segment Definition)
22
Directives
;THE FORM OF AN ASSEMBLY LANGUAGE PROGRAM USING SIMPLIFIED SEGMENT DEFINITION .MODEL SMALL .STACK 64 .DATA ; ;place data definitions here ; .CODE MAIN PROC FAR ;this is the program entry point MOV AX,@DATA ;load the data segment address MOV DS,AX ;assign value to DS ; ;place code here ; MOV AH,4CH ;set up to INT 21H ;return to DOS MAIN ENDP END MAIN ;this is the program exit point
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2102440 Introduction to Microprocessors
¾
PAGE and TITLE z z
z
z
PAGE [lines], [column] Æ tell the printer how the list should be printed. Default setting PAGE (no numbers after it): 66 lines per page and and max. 80 characters PAGE 60,132 Æ the range of number of lines = 10 t0 255 and range of columns = 60 to 132. TITLE Æ put the name of the program and a brief description of the function function of the program.
¾
.STACK ; marks the beginning of the stack segment .DATA ; marks the beginning of the data segment .CODE; marks the beginning of the code segment
¾
.STACK 64 ; reserves 64 bytes of memory for the stack
¾ ¾
mov ax,@data ; data refers to the start of the data segment mov ds,ax 23
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4
Control Transfer Instructions
8086 Conditional Jump (I)
¾ To transfer program control to a different
location. z
NEAR: control transfer within the current code segmentÆ segmentÆ intrasegment (within segment) - A NEAR jump Æ IP is updated; CS remains the same.
z
FAR: control transfer outside the current code segment Æ intersegment (between segment) - A FAR jump Æ both IP and CS are updated.
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8086 Conditional Jump (II) Mnemonic
Condition Tested
“Jump IF …”
JLE/JNG
((SF xor OF) or ZF) = 1
less or equal/not greater
JNC
CF = 0
not carry
JNE/JNZ
ZF = 0
not equal/not zero
JNO
OF = 0
not overflow
JNP/JPO
PF = 0
not parity/parity odd
JNS
SF = 0
not sign
JO
OF = 1
overflow
JP/JPE
PF = 1
parity/parity even
JS
SF = 1
sign 2102440 Introduction to Microprocessors
above/not below nor zero
JAE/JNB
CF = 0
above or equal/not below
JB/JNAE
CF = 1
below/not above nor equal
JBE/JNA
(CF or ZF) = 1
below or equal/not above
JC
CF = 1
carry
JE/JZ
ZF = 1
equal/zero
JG/JNLE
((SF xor OF) or ZF) = 0
greater/not less nor equal
JGE/JNL
(SF xor OF) = 0
greater or equal/not less
JL/JNGE
(SF xor OF) = 1
less/not greater nor equal
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-128 to +127 bytes of the IP (256 possible addresses). ¾ - for the backward jump and + for the forward jump.
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CALL statements • CALL instruction is used to call a procedure.
SHORT JUMP Æ “JMP SHORT label” label” (-128 to 127 bytes) NEAR JUMP Æ “JMP label” label” (within the current code segment); the target address can be any of the addressing modes of direct, register, or register indirect. FAR JUMP Æ “JMP FAR PTR label” label” (CS and IP are replaced with new values) 2102440 Introduction to Microprocessors
“Jump IF …”
¾ The address of the target must be within
“JMP label” label” ¾ To transfer unconditionally to the target location label.
•
(CF = 0) and (ZF = 0)
¾ All conditional jumps are short jumps.
¾
•
Condition Tested
JA/JNBE
Short Jumps
Unconditional jump
•
Mnemonic
29
• NEAR call Æ within the current code segment. Only IP is saved on the stack. • FAR call Æ> outside the current code segment. Both CS and IP are saved on the stack.
;------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------MAIN PROC FAR ; This is the entry point for DOS MOV AX,@DATA MOV DS, AX CALL SUBR1 CALL SUBR2 MOV AH,4cH INT 21H MAIN ENDP ;------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------SUBR1 PROC ... ... RET SUBR1 ENDP ;------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------SUBR2 PROC ... ... RET SUBR2 ENDP ;------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------END MAIN ; This is the exit point
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5
Unsigned Addition and Subtraction ¾
Executing an Assembly Program ¾
ADD destination, source ;
¾
dest. dest. operand = dest. dest. operand + source operand
¾
¾
Dest. Dest. Operand = dest. dest. Operand + source operand + carry
The destination operand can be a register or in memory. The source operand can be a register, in memory, or immediate. MemoryMemory-toto-memory operations are not ALLOWED in 80x86.
z
z
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Write a program calculates the total sum of 5 bytes of data. Each byte represents the daily wages of a worker. This person does not make more than $255 (FFH) a day. The decimal data is as follows: 125, 235, 197, 91, 48.
33
Sample Program 1 (cont.)
BACK:
OVER:
MAIN
PROC MOV MOV MOV MOV MOV ADD JNC INC INC DEC JNZ MOV MOV INT ENDP END
FAR AX,@DATA DS,AX CX,COUNT SI,OFFSET DATA AX,00 AL,[SI] OVER AH SI CX BACK SUM,AX AH,4CH 21H
Run the Linker to generate an .EXE file from the .OBJ file
3. ¾
tlink yourfile
Run the Program
4. ¾
Your final program (if there were no errors in the previous step) step) will have an .EXE ending. To just run it, type: yourfile
If want to debug your program
5. ¾
td yourfile
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;This program calculates the total sum of 5 bytes of data. Each byte represents the daily wages ; of a worker. This person does not make more than $255 (FFH) a day
Example 1: Addition of individual byte and word data
.CODE MAIN
tasm /z/zi yourfile.asm (The /z switch causes TASM to display the lines that generate compilation errors. The /zi /zi switch enables information needed by the debugger to be included in the .OBJ file.) file.)
Sample Program 1
Assembly Program Example 1
2102440 Introduction to Microprocessors
notepad yourfile.asm wordpad yourfile.asm edit yourfile.asm
Compile the source code to create an object module
2.
ADC destination, source; z
Edit yourfile.asm using one of the follows:
1.
Addition of unsigned numbers
TITLE PROG3PROG3-1A (EXE) ADDING 5 BYTES PAGE 60,132 .MODEL SMALL .STACK 64 ;-------------.DATA COUNT EQU 05 DATA DB 125,235,197,91,48 ORG 0008H SUM DW ? ;-------------2102440 Introduction to Microprocessors
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Assembly Program Example 2 Example 2: Addition of multiword numbers
;CX is the loop counter ;SI is the data pointer ;AX will hold the sum ;add the next byte to AL ;If no carry, continue ;else accumulate carry in AH ;increment data pointer ;decrement loop counter ;if not finished, go add next byte ;store sum
Write a program to calculate the total sum of five words of data. Each data represents the yearly wages of a worker. This person does not make more than $65,555 (FFFFH) a year. The decimal data are 27345, 28521, 29533, 30105, and 32375.
;go back to DOS
MAIN
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6
Sample Program 2
Sample Program 2 (cont.)
;This program calculates the total sum of five words of data. Each Each data value represents the yearly ; wages of a worker. This person does not make more than $65,555 $65,555 (FFFFH) a year TITLE PROG3PROG3-1B (EXE) ADDING 5 WORDS PAGE 60,132 .MODEL SMALL .STACK 64 ;-------------.DATA COUNT EQU 05 DATA DW 27345,28521,29533,30105,32375 ORG 0010H SUM DW 2 DUP(?) ;-------------2102440 Introduction to Microprocessors
.CODE MAIN
BACK:
MAIN
37
PROC MOV MOV MOV MOV MOV MOV ADD ADC INC INC DEC JNZ MOV MOV MOV INT ENDP END
FAR AX,@DATA DS,AX CX,COUNT SI,OFFSET DATA AX,00 BX,AX AX,[SI] BX,0 SI SI CX BACK SUM,AX SUM+2,BX AH,4CH 21H
;CX is the loop counter ;SI is the data pointer ;AX will hold the sum ;BX will hold the carries ;add the next word to AX ;add carry to BX ;increment data pointer twice ;to point to next word ;decrement loop counter ;if not finished, continue adding ;store the sum ;store the carries ;go back to DOS
MAIN
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7
