8086 Microprocessor u2

CS601: Microprocessor & Interfacing : UNIT 2

X86 Programming model• Instruction Set Architecture (ISA) : the definition of the

registers and instructions that define the programmer’s view of a processor

• Can have different implementations of the same ISA– Intel and AMD processors both execute the x86 ISA, but internally are

very different!!– Intel has several different implementations of the x86 ISA!

• New versions of an ISA extend the previous version by adding instructions, registers – but never invalidate the old ISA

2/27/2010 Arvind Shrivastava 2

Intel x86 Microprocessors8086 - 20 bit Addr. Bus - 1MB of Memory

80286 - 24 Addr. Bus - Added Protection Mode

80386 - 32 bit regs/busses - Virtual 86 Mode

80486 - RISC Core - L1 Cache - FPU

Pentium - Superscalar - Dual Pipeline - Split L1 Cache

Pentium Pro - L2 Cache - Branch Pred. - Speculative Exec.

Pentium MMX - 57 Instructions - Integrated DSP (MMX)

Pentium II - 100 MHz Bus - L2 Cache - MMX

Celeron - 66 MHz Bus - True L2 Cache Integration

Pentium III - 100 MHz Bus - 70 Internet Streaming SIMD

Ext.2/27/2010 Arvind Shrivastava 3

8086 Register File


CSDSSSES

AHBHCHDH

ALBLCLDL

IPSPBPSIDI

07

015

07

015

Accumulator

Base

Counter

Data

Code Segment

Data Segment

Stack Segment

Extra Segment

Instruction Pointer

Stack Pointer

Base Pointer

Source Index

Destination Index

}

}}

AXBXCXDX

8086 Register File Contd..

• IP Contains Address of NEXT Instruction to be Fetched– Automatically Incremented– Programmer can control with jump and branch


015

Instruction Pointer Register

AX, BX, CX, DX


• General Purpose Registers

AHBHCHDH

ALBLCLDL

07 07

Accumulator

Base

Counter

Data

AXBXCXDX

• Can Be Used Separately as 1-byte Registers

AX = AH:AL• Temporary Storage to Avoid Memory Access

– Faster Execution – Avoids Memory Access

• Some Special uses for Certain Instructions

AX, BX, CX, DX - Some Specialized Uses


• AX, Accumulator

– Main Register for Performing Arithmetic

– mult/div must use AH, AL

– “accumulator” Means Register with Simple ALU

• BX, Base

– Point to Translation Table in Memory

– Holds Memory Offsets; Function Calls

• CX, Counter

– Index Counter for Loop Control

• DX, Data

– After Integer Division Execution - Holds Remainder

CS, DS, ES, SS - Segment Registers


Contains “Base Value” for Memory Address

CS, Code SegmentUsed to “point” to InstructionsDetermines a Memory Address (along with IP)Segmented Address written as CS:IP

DS, Data SegmentUsed to “point” to DataDetermines Memory Address (along with other registers)ES, Extra Segment allows 2 Data Address Registers

SS, Stack SegmentUsed to “point” to Data in Stack Structure (LIFO)Used with SP or BPSS:SP or SS:BP are valid Segmented Addresses

IP, SP, BP, SI, DI - Offset Registers


IP, Instruction PointerUsed to “point” to InstructionsDetermines a Memory Address (along with CS)Segmented Address written as CS:IP

SI, Source Index; DI, Destination IndexUsed to “point” to DataDetermines Memory Address (along with other registers)DS, ES commonly used

SP, Stack Pointer; BP, Base PointerUsed to “point” to Data in Stack Structure (LIFO)Used with SSSS:SP or SS:BP are valid Segmented Addresses

Contains “Index Value” for Memory Address

INSTRUCTION SET OF 8086 Classified into 7 categories1] Data Transfer 2] Arithmetic 3] Logical 4] Control 5]Processor Control Instructions6] String Manipulation7] Interrupt Control


Data Transfer Instructions Note: Data Transfer Instructions do not affect any flags1] MOV dest, srcNote that source and destination can not be memory

location. Also source and destination must be same type.

2] PUSH Src: Copies word on stack.3] POP dest: Copies word from stack into dest. Reg.4] INacc, port : Copies 8 or 16 bit data from port to

accumulator. a) Fixed Port b) Variable Port 5] OUTport,acc


Data Transfer Instructions Contd… 6] LESReg, Mem: Load register and extra segment

register with words from memory.7] LDSReg,Mem: Load register and data segment

register with words from memory.8] LEAReg,Src: load Effective address. (Offset is loaded

in specified register)9] LAHF: Copy lower byte of flag register into AH

register.10] SAHF: Copy AH register to lower byte of flag

register


Data Transfer Instructions Contd…

11] XCHG dest, src: Exchange contains of source and destination.

12] XLAT: Translate a byte in AL. This instruction replaces the byte in AL with byte pointed by BX.To point desired byte in look up table instruction adds contains of BX with AL ( BX+ AL). Goes to this location and loads into AL.


Arithmetic Instructions 1]ADD dest,src 2] ADC dest,src: Add with carry3] AAA : ASCII adjust after addition. We can add

two ASCII numbers directly and use AAA after addition so as to get result directly in BCD. (Works with AL only)

4] DAA : Decimal adjust accumulator. ( Works with AL only)

5] SUB dest, src6] SBB dest, src: Subtract with borrow.2/27/2010 Arvind Shrivastava 14

Arithmetic Instructions Contd … 7] AAS: ASCII adjust for subtraction ( Same as

AAA and works with AL only)8] DAS : Decimal adjust after Subtraction.

(Works with AL only)9] MUL src10 ] IMULsrc: Multiplication of signed byte.11] AAM: BCD adjust after multiply. ( Works

with AL only)12]DIV src If any one attempts to divide by 0 , then ?2/27/2010 Arvind Shrivastava 15

Arithmetic Instructions Contd … 13] IDIV: Division of signed numbers14]AAD: BCD to Binary convert before Division.15] DEC dest16] INCdest17] CWD: Convert signed word to signed double

word.18] CBW : Convert signed byte to signed word.

( CBW and CWD works only with AL,AX and DX registers.)

• 19] NEG dest: Forms Twos complement.2/27/2010 Arvind Shrivastava 16

Logical Instructions1] AND dest,src2] NOT dest: Invert each bit in destination3] OR dest, src4] XOR dest, src5] RCL dest, count : Rotate left through Carry If rotate once

count is directly specified in the instruction. For more no. of rotations count is specified in CL register.

6] RCR dest, count : Rotate right through carry7] ROL dest, count : Rotate left (into carry as well as into LSB)8] ROR dest, count : Rotate left (into carry as wellas into

MSB)


Logical Instructions Contd…9] SAL/ SHL dest, count : Shift left and put 0in LSB.10] SAR dest,count : Shift right New MSB = Old MSB11]SHR dest,count : Shift right .MSB is filled with 0’s.12] TEST dest,src: AND logically,updates flags but

source and destare unchanged.13] CMP dest,srcCF, ZF and SF are used Ex .CMP CX,BX


CF ZF SF

CX = BX 0 1 0

CX > BX 0 0 0

CX < BX 1 0 1

Control transfer Instructions1]CALL : Call a procedure - Two types of calls

i) Near Call ( Intrasegment)ii) Far Call ( Intersegment)

2] RET : Return execution from procedure3] JMP : Unconditional Jump to specified

destination. Two types near and Far4] JA / JNBE: Jump if above / Jump if not below• The terms above and below are used when we

refer to the magnitude of Unsigned number . Used normally after CMP.

5]JAE / JNB / JNC2/27/2010 Arvind Shrivastava 19

Control Transfer Inst. Contd…6] JB / JC / JNAE7] JBE / JNA8] JE/ JZ9]JCXZ: Jump if CX is Zero.10] JG / JNLE: Jump if Greater /Jump if not less than or

equal. The term greater than or less than is used in connection with two signed numbers.

• 11] JGE / JNL:• 12] JL / JNGE :• 13] JLE / JNG :• 14]JNE / JNZ :


Control Transfer Inst. Contd…15] JNO : Jump if no overflow16] JNS :Jump if no sign17] JS18] JO19] JNP / JPO 20] JP / JPE

In all above conditional instructions the destination of jump is in the range of -128 to + 127 bytes from the address after jump.


Control Transfer Inst. Contd…21] LOOP: Loop to the specified label if CX not equal

to Zero. The count is loaded in CX reg. Every time LOOP is executed then CX is automatically decremented . ( Used in delay programs.)

22] LOOPE/ LOOPZ: Loop while CX not equal to zero and ZF = 1.

23] LOOPNE / LOOPNZ: Loop while CX not equal to zero and ZF = 0.

In all above LOOP instructions the destination of jump is in the range of -128 to + 127 bytes from the address after LOOP.


Processor Control1] CLC: Clear Carry flag.2] STC : Set carry Flag3] CMC : Complement Carry Flag4] CLD: Clear Direction Flag.5] STD: Set Direction Flag6] CLI : Clear Interrupt Flag.7] STI : Set Interrupt Flag.8] HLT: Halt Processing.


Processor Control Contd…

9] NOP : No Operation10] ESC: Escape, Executed by Co-processors and

actions are performed according to 6 bit coding in the instruction.

11] LOCK : Assert bus lock Signal, This is prefix instruction.

12] WAIT :Wait for test or Interrupt Signal. Assert wait states.


String Control1] MOVS/ MOVSB/ MOVSW : Dest string name, src

string name. This inst moves data byte or word from location in DS to location in ES.

2] REP / REPE / REPZ / REPNE / REPNZ: Repeat string instructions until specified conditions exsist. This is prefix instruction.

3] CMPS / CMPSB / CMPSW: Compare string bytes or string words.

4] SCAS / SCASB / SCASW: Scan a string byte or string word. Compares byte in AL or word in AX. String address is to be loaded in DI.


String Control Contd…

5] STOS / STOSB / STOSW: Store byte or word in a string. Copies a byte or word in AL or AX to memory location pointed by DI.

6] LODS / LODSB /LODSW : Load a byte or word in AL or AX Copies byte or word from memory location pointed by SI into AL or AX register.


Interrupt Control

• 1]INT type• 2] INTO Interrupt on overflow• 3] IRET Interrupt return


Assembler Directives

1] ASSUME : Used to tell assembler the name of logical segment. Ex. ASSUME CS: Code here

2] END 3] DB4] DW5] DD Define Double Word6] DQ Define Quad Word7] DT Define Ten Bytes2/27/2010 Arvind Shrivastava 28

Assembler Directive Contd..8] PROC Procedure : PROC DELAY NEAR9] ENDP10] ENDS11] EQU12] EVEN: Align on even memory address.13] ORG 14] OFFSET: Ex MOV BX,Offset of Data Here15] PTR Pointer16] LABEL : Ex AGAIN LABEL FAR17] EXTRN: Tells the assembler that the names or labels

following this directive is in some other assembly module.


Assembler Directive Contd..18] PUBLIC : Links modules together19] INCLUDE : Include source code from file.20] NAME : To give specific name to module.21] GROUP : Grouping of logical segments.22] SEGMENT23] SHORT : Operator that tells assembler about

short displacement.24] TYPE : Type of variable whether byte or

word.


Data Transfer• IN AL,0C8H ;Input a byte from port 0C8H to

;AL• IN AX, 34H ;Input a word from port 34H to• AXA_TO_D EQU 4AH• IN AX, A_TO_D ;Input a word from port

;4AH to AX• MOV DX, 0FF78H ;Initialize DX point to port• IN AL, DX ;Input a byte from a 8 bit port

;0FF78H to AL• IN AX, DX ;Input a word from 16 bit port to

;0FF78H to AX.


Arithmetic Instruction• EXAMPLE: • ADD AL,74H ;Add immediate number 74H

;to content of AL• ADC CL,BL ;Add contents of BL plus

;carry status to contents of CL. ;Results in CL

• ADD DX, BX ;Add contents of BX to ;contents of DX

• ADD DX, [SI] ;Add word from memory at ;offset [SI] in DS to contents of DX


Logical instruction• OR op1, op2• OR AH, CL ;CL ORed with AH, result in AH.

;CX = 00111110 10100101• OR CX,FF00h ;OR CX with immediate FF00h

;result in CX = 1111111110100101;Upper byte are all 1’s lower bytes;are unchanged

• ;DX =F038h• NOT DX ;after the instruction DX = 0FC7h


Control transfer Instruction• ;Direct within-segment - near• CALL MULTO ;MULTO is the name ofthe

;procedure.

• ;Indirect within-segment -near• CALL BX ; BX contains the offset of the first

instruction of the procedure .Replaces contents of word of IP with contents o register BX.


Control transfer contd..

• ;Direct to another segment- far• CALL SMART ;SMART is the name of the

;Procedure• SMART PROC FAR ; Procedure must be

;declared as an far• RET Instruction – Return execution from

procedure to calling program


Program to multiply two 16bit binary no. & give 32 bit result

;ABSTRACT This program multiplies two 16bit words in the memory locations called MULTIPLICAND and MULTIPLIER. Result is stored in memory location , PRODUCT.

;REGISTERS : Uses CS, DS, AX, DXDATA_HERE SEGMENT

MULTIPLICAND DW 204AH ; first word hereMULTIPLIER DW 3B2AH ; second word herePRDUCT DW 2 DUP(0) ; Result of

multiplication hereDATA_HERE ENDS


Program Contd..CODE_HERE SEGMENT

ASSUME CS:CODE_HERE, DS:DATA_HERESTART:MOV AX, DATA_HERE ;Initialize DS

MOV DS, AX ; registerMOV AX, MULTIPLICAND ; Get one wordMUL MULTIPLIER ; Multiply by 2nd wordMOV PRODUCT, AX ;Store low word of resultMOV PRODUCT+2, DX ; Store high word of resultINT 3 ; wait for command from user

CODE_HERE ENDSEND START


JUMP, FLAGS and conditional Jumps• 8086 fetches next instruction from some new

location• JMP always causes a jump to occur• Loads a new no. into IP register• Sometimes CS is also loaded with new no.• Direct or indirect jump, destination address• Program should be relocatable


Backward Jump;ABSTRACT : This program illustrates a backward

jump;REGISTERS : Uses CS, AL; PORTS : None CODE SEGMENT

ASSUME CS:CODEBACK: ADD AL, 03H

NOPNOPJMP BACK

CODE ENDSEND2/27/2010 Arvind Shrivastava 39

Forward Jump;ABSTRACT : Program illustrates forward jump;REGISTERS : Uses CS, AX;PORS : None

CODE SEGMENTASSUME CS: CODEJMP THERENOPNOP

THERE: MOV AX, 0000HNOPENDSEND2/27/2010 Arvind Shrivastava 40

8086 conditional flags- Six conditional Flags: Carry Flag (CF), parity flag (PF),

auxiliary carry flag (AF), zero flag(ZF), sign flag(SF), overflow flag(OF).

- Carry Flag is affected by ADD, SUB, AND , CMP instructions

- CMP BX, CXCondition CF ZFCX > BX 1 0CX<BX 0 0CX=BX 0 1


Conditional flags contd..• AF: DAA, DAS instructions• ZF: INC, DEC, CMP inst.• OF:ADD


Conditional Jump• All conditional jump instructions are short-

type jumps. • Destination address must be in the range -128

to +127• Destination label must be in the same code

segment


Conditional jump contd..JE /JZ ZF = 1 Jump if Equal or Jump if Zero (=)JNE/JNZ ZF = 0 Jump if Not Equal or Jump if Not

ZeroSigned ComparisonsJG ZF = 0 and SF = 0 Jump if Greater than ( > )JGE SF = 0 Jump if Greater than or Equal

( >= )JL SF = 1 Jump if Less than ( < )JLE ZF = 1 or SF = 1 Jump if Less than or Equal ( <=)


Conditional jump contd..Unsigned ComparisonsJA ZF = 0 and CF = 0 Jump if Above ( > )JAE CF = 0 Jump if Above or Equal ( >= )JB CF = 1 Jump if Below ( < )JBE ZF = 1 or CF = 1 Jump if Below or Equal ( <= )MiscellaneousJO OF = 1 Jump if Overflow, ditto for CF, SF &

PFJNO OF = 0 Jump if No Overflow, ditto for

CF, SF & PFJCXZ CX = 0 Jump if CX = 0JECXZ ECX = 0 Jump if ECX = 02/27/2010 Arvind Shrivastava 45

IF-THENIf <condition> THEN CMP AX,BX

action JE THERE…… ADD AX, 0020H

THERE: MOV CL, 20H

CMP AX, BXJNE FIXJMP THEREFIX: ADD AX, 0020HTHERE: MOV CL, 07H2/27/2010 Arvind Shrivastava 46

IF-THEN-ELSEREAD TEMPERATUREIF TEMPERATURE < 30 THEN

LIGHT YELLOW LAMPELSE

LIGHT GREEN LAMPREAD pH SENSOR

IF TEMPERATURE ≥ 30 THENLIGHT GREENLAMP

ELSELIGHT YELLOWLAMP

READ SENSOR


IF-THEN-ELSE contd…;ABSTRACT : this program reads the temp, if temp < 30, a

yellow lamp is lit, if temp is ≥ 30, a green lamp is lit;REGISTERS : CS, AL, DX;PORTS : FFF8H – temp I/P, FFFAH – Control O/P

CODE SEGMENTASSUME CS: CORE

; intialize port FFFAH as O/P and FFF8H as I/PMOV DX, 0FFFEH ; point DX to port control regsMOV AL, 99H ; Load control word to initialize portsOUT DX, AL ; send control word to port control regs


IF-THEN-ELSE contd…MOV DX, 0FFF8H ; point DX at I/P portIN AL, DX ; read temp from sensor on I/P portCMP AL, 30JB YELLOWJMP GREEN

YELLOW : MOV AL, 01H ; load code to light yellow

MOV DX, 0FFFAH ; point DX at O/P portOUT DX, AL ; send code to light yellow lampJMP EXIT ; go to exit mainline instructions


IF-THEN-ELSE contd…GREEN: MOV AL, 02H ; load code to light green

MOV DX, 0FFFAH ; point DX at O/P portOUT DX, AL ; send code to light green lamp

EXIT : MOV DX, 0FFFCH ; next mainline instIN AL, DX ; read pH sensor

CODE ENDSEND


IF-THEN-ELSE contd…ALGO (B)…..

CMP AL, 30 ; compare temp with 30JAE GREEN ; if temp ≥ 30 then light greenJMP YELLOW ; ELSE light YELLOW

GREEN : MOV AL, 02H ; load code to light green lampMOV DX, 0FFFAH ; point DX at O/P portOUT DX, AL ; send code to light greenJMP EXIT ; go to next mainline instruction


IF-THEN-ELSE contd…YELLOW: MOV AL, 01H ; Load code to light

yellowMOV DX, 0FFFAH ; point DX at O/P portOUT DX, AL ; send code to light yellow

EXIT : MOV DX, 0FFFCH ; next mainline instruction

IN AL, DX ; Read pH sensorCODE ENDS

END


Think about

1. How high level language statements are translated to 8086 instructions

2. How logical operations can be used to set and clear bits

3. Execution/Implementation of IF-THEN, IF-THEN-ELSE,REPEAT-UNTIL,LOOP,WHILE in assembly language.


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8086 Microprocessor u2