Assembly Language Programming Part 2

Assembly Language Programming

Part 2

• Microprocessor’s Instruction Set

Microprocessor’s Instruction Set

• An instruction set is a list of all the instructions, and all their variations, that a processor (or in the case of a virtual machine, an interpreter) can execute.

• an instruction is a single operation of a processor defined by an instruction set architecture.

• On traditional architectures, an instruction includes

• An opcode specifying the operation to be performed, such as "add contents of memory to register",

• zero or more operand specifiers, which may specify registers, memory locations, or literal data. The operand specifiers may have addressing modes determining their meaning or may be in fixed fields.

Microprocessor’s Instruction Set

• Instructions include:

• Arithmetic such as add and subtract

• Logic instructions such as and, or, and not

• Data instructions such as move, input, output, load, and store

• Control flow instructions such as goto, if ... goto, call, and return.

MOVCopy operand2 to operand1.The MOV instruction cannot:•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). •copy immediate value to segment register (should copy to general register first).

Operands Algorithm Examples

REG, memorymemory, REGREG, REGmemory, immediateREG, immediate

SREG, memorymemory, SREGREG, SREGSREG, REG

operand1 = operand2

FLAGS MOV has no impact on FLAGS register

MOV AL,[0100]MOV [0100],AHMOV AX,BXMOV [0200],5MOV BL,0EH

MOV DS, MyVar *MOV MyVar, CSMOV AX,ESMOV SS,DX

* MyVar is a variable of size 2 bytes (Not available in Debug)

ADD

Add


REG, memorymemory, REGREG, REGmemory, immediateREG, immediate operand1 = operand1 + operand2

FLAGS

ADD AL,[0105]ADD [0100],AHADD BX,CXADD [0200],5ADD BL,1AH

ADD AL, MyVar *ADD MyVar, DX **

* MyVar is a variable of size 1 bytes.

** MyVar is a variable of size 2 bytes.

INC

Increment.


REGmemory

operand = operand + 1

FLAGS

CF-Not changed

INC ALINC [0100]

INC SIINC CXINC MyVar *

* MyVar is a variable of any size

SUB

Subtract


REG, memorymemory, REGREG, REGmemory, immediateREG, immediate operand1 = operand1 - operand2

FLAGS

SUB AL,[0105]SUB [0100],AHSUB BX,CXSUB [0200],5SUB BL,1AH

SUB AL, MyVar *SUB MyVar, DX **



DEC

Decrement.


REGmemory

operand = operand - 1

FLAGS

CF-Not changed

DEC ALDEC [0100]

DEC SIDEC CXDEC MyVar *


MUL

Unsigned multiply.


REGmemory

when operand is a byte:AX = AL * operand.

when operand is a word (2 Bytes):(DX AX) = AX * operand.

FLAGS

CF=OF=0 when high section of the result is zero.

MUL BLMUL [0302]

MUL BXMUL MyVar *


IMUL

Signed multiply.


REGmemory

when operand is a byte:AX = AL * operand.

when operand is a word (2 Bytes):(DX AX) = AX * operand.

FLAGS

CF=OF=0 when result fits into operand of IMUL.

IMUL BLIMUL [0302]

IMUL BXIMUL MyVar *


DIV

Unsigned divide.


REGmemory

when operand is a byte:AL = AX / operandAH = remainder (modulus)

when operand is a word:AX = (DX AX) / operandDX = remainder (modulus)

FLAGS

DIV BLDIV [0302]

DIV BXDIV MyVar *


IDIV

Signed divide.


REGmemory

when operand is a byte:AL = AX / operandAH = remainder (modulus)

when operand is a word:AX = (DX AX) / operandDX = remainder (modulus)

FLAGS

IDIV BLIDIV [0302]

IDIV BXIDIV MyVar *


NEG

Negate. Makes operand negative (two's complement).


REGmemory Invert all bits of the operand

Add 1 to inverted operand

FLAGS

NEG BLNEG [0302]

NEG BXNEG DINEG MyVar *


NOP

No Operation.


No OperandsDo nothing

FLAGS NOP

NOT

Invert each bit of the operand.


REGmemory if bit is 1 turn it to 0.

if bit is 0 turn it to 1.

FLAGS

NOT BLNOT [0302]

NOT BXNOT DINOT MyVar *


AND

Logical AND.



Logical AND between all bits of two operands. Result is stored in operand1.

These rules apply:1 AND 1 = 11 AND 0 = 00 AND 1 = 00 AND 0 = 0

FLAGS

AND AL,[0105]AND [0100],AHAND BX,CXAND [0200],5AND BL,1AH

AND AL, MyVar *AND MyVar, DX **



OR

Logical OR.



Logical OR between all bits of two operands. Result is stored in first operand.

These rules apply:1 OR 1 = 11 OR 0 = 10 OR 1 = 10 OR 0 = 0

FLAGS

OR AL,[0105]OR [0100],AHOR BX,CXOR [0200],5OR BL,1AH

OR AL, MyVar *OR MyVar, DX **



XOR

Logical OR.



Logical XOR (Exclusive OR) between all bits of two operands. Result is stored in first operand.

These rules apply:1 XOR 1 = 01 XOR 0 = 10 XOR 1 = 10 XOR 0 = 0

FLAGS

XOR AL,[0105]XOR [0100],AHXOR BX,CXXOR [0200],5XOR BL,1AH

XOR AL, MyVar *XOR MyVar, DX **



SHL

Shift operand1 Left. The number of shifts is set by operand2.


memory, immediateREG, immediate

memory, CLREG, CL

Shift all bits left, the bit that goes off is set to CF. Zero bit is inserted to the right-most position.

FLAGS

OF=0 if first operand keeps original sign.

SHL [0105],2SHL AH, 3

SHL [0200],CLSHL BX, CL

SHL MyVar, 4 *SHL MyVar, CL *


SHR

Shift operand1 Right. The number of shifts is set by operand2.



memory, CLREG, CL

Shift all bits right, the bit that goes off is set to CF. Zero bit is inserted to the left-most position.

FLAGS


SHR [0105],2SHR AH, 3

SHR [0200],CLSHR BX, CL

SHR MyVar, 4 *SHR MyVar, CL *


ROL

Rotate operand1 left. The number of rotates is set by operand2.



memory, CLREG, CL

shift all bits left, the bit that goes off is set to CF and the same bit is inserted to the right-most position.

FLAGS


ROL [0105],2ROL AH, 3

ROL [0200],CLROL BX, CL

ROL MyVar, 4 *ROL MyVar, CL *


ROR

Rotate operand1 right. The number of rotates is set by operand2.



memory, CLREG, CL

shift all bits right, the bit that goes off is set to CF and the same bit is inserted to the left-most position.

FLAGS


ROR [0105],2ROR AH, 3

ROR [0200],CLROR BX, CL

ROR MyVar, 4 *ROR MyVar, CL *


XCHG

Exchange values of two operands.


REG, memorymemory, REGREG, REG operand1 < - > operand2

FLAGS

XCHG AL,[020E]XCHG [020E], ALXCHG AX,BX

XCHG DL,MyVar *XCHG MyVar, BP **

* MyVar is a variable of size Byte

** MyVar is a variable of size Word

PUSH

Store 16 bit value in the stack.Note: PUSH immediate works only on 80186 CPU and later!


REGSREGmemoryimmediate

SP = SP - 2 SS:[SP] (top of the stack) = operand

FLAGS

PUSH AXPUSH CSPUSH [020E]PUSH 1AH

PUSH MyVar *


POP

Get 16 bit value from the stack.


REGSREGmemory

operand = SS:[SP] (top of the stack) SP = SP + 2

FLAGS

POP AXPOP CSPOP [020E]

POP MyVar *


LOOP

Decrease CX, jump to label if CX not zero.


Label/address CX = CX - 1if CX <> 0 then jump else no jump, continue

FLAGS

MOV CX,5label1:; Some CodeLOOP label1

CS:0100 MOV CX,5CS:0103 INC SI; Some CodeCS:107 LOOP 103

CMP

Compare.



operand1 - operand2

result is not stored anywhere, flags are set (OF, SF, ZF, AF, PF, CF) according to result.

FLAGS

CMP DL,[021A]CMP [021A], CLCMP AX, DXCMP [012A], 12HCMP BL,0FH

CMP DL,MyVar *CMP MyVar, BX **

* MyVar is a variable of size Byte

** MyVar is a variable of size Word

JMP

Unconditional Jump. Transfers control to another part of the program. 4-byte address may be entered in this form: 1234h:5678h, first value is a segment second value is an offset.


Labeladdress/4-byte

addressalways jump

FLAGS

label1:; Some CodeJMP label1

CS:0100 JMP 104; Some CodeCS:0104 INC SI

JE

Short Jump if first operand is Equal to second operand (as set by CMP instruction). Signed/Unsigned.


Labeladdress

if ZF = 1 then jump else continue

FLAGS

CMP AL,BLJE label1; Code to skip if ZF = 0label1:; Code to execute if ZF = 1

CS:0100 CMP AL,BLCS:0102 JE 107; Code to skip if ZF = 0CS:0107 INC SI; Code to execute if ZF = 1

JNE

Short Jump if first operand is Not Equal to second operand (as set by CMP instruction). Signed/Unsigned.


Labeladdress


FLAGS

CMP AL,BLJNE label1; Code to skip if ZF = 1label1:; Code to execute if ZF = 0

CS:0100 CMP AL,BLCS:0102 JNE 107; Code to skip if ZF = 1CS:0107 INC SI; Code to execute if ZF = 0

JZ

Short Jump if Zero (equal). Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.


Labeladdress


FLAGS

CMP AL,BLJZ label1; Code to skip if ZF = 0label1:; Code to execute if ZF = 1

CS:0100 CMP AL,BLCS:0102 JZ 107; Code to skip if ZF = 0CS:0107 INC SI; Code to execute if ZF = 1

JNZ

Short Jump if Not Zero (not equal). Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.


Labeladdress


FLAGS

CMP AL,BLJNZ label1; Code to skip if ZF = 1label1:; Code to execute if ZF = 0

CS:0100 CMP AL,BLCS:0102 JNZ 107; Code to skip if ZF = 1CS:0107 INC SI; Code to execute if ZF = 0

JA

Short Jump if first operand is Above second operand (as set by CMP instruction). Unsigned.


Labeladdress

if (CF = 0) and (ZF = 0) then jump else continue

FLAGS

CMP AL,BLJA label1; Code to skip if CF <> 0 and ;ZF <> 0label1:; Code to execute if CF = 0 and;ZF = 0

CS:0100 CMP AL,BLCS:0102 JA 107; Code to skip if CF <> 0 and ;ZF <> 0CS:0107 INC SI; Code to execute if CF = 0 and;ZF = 0

JNA

Short Jump if first operand is Not Above second operand (as set by CMP instruction). Unsigned.


Labeladdress

if CF = 1 or ZF = 1 then jump else continue

FLAGS

CMP AL,BLJNA label1; Code to skip if CF <> 1 and ;ZF <> 1label1:; Code to execute if CF = 1 and;ZF = 1

CS:0100 CMP AL,BLCS:0102 JNA 107; Code to skip if CF <> 1 and ;ZF <> 1CS:0107 INC SI; Code to execute if CF = 1 and;ZF = 1

JAE

Short Jump if first operand is Above or Equal to second operand (as set by CMP instruction). Unsigned.


Labeladdress

if CF = 0 then jump else continue

FLAGS

CMP AL,BLJAE label1; Code to skip if CF <> 0label1:; Code to execute if CF = 0

CS:0100 CMP AL,BLCS:0102 JAE 107; Code to skip if CF <> 0CS:0107 INC SI; Code to execute if CF = 0

JNAE

Short Jump if first operand is Not Above and Not Equal to second operand (as set by CMP instruction). Unsigned.


Labeladdress

if CF = 1 then jump else continue

FLAGS

CMP AL,BLJNAE label1; Code to skip if CF <> 1label1:; Code to execute if CF = 1

CS:0100 CMP AL,BLCS:0102 JNAE 107; Code to skip if CF <> 1CS:0107 INC SI; Code to execute if CF = 1

JB

Short Jump if first operand is Below second operand (as set by CMP instruction). Unsigned.

Operands Algorithm Example

Labeladdress

if CF = 1 then jump

include 'emu8086.inc' ORG 100h MOV AL, 1 CMP AL, 5 JB label1 PRINT 'AL is not below 5' JMP exit

label1: PRINT 'AL is below 5' exit: RET

JBE

Short Jump if first operand is Below or Equal to second operand (as set by CMP instruction). Unsigned.


Labeladdress

if CF = 1 or ZF = 1 then jump

include 'emu8086.inc' ORG 100h MOV AL, 5 CMP AL, 5 JBE label1PRINT 'AL is not below or equal to 5' JMP exit label1: PRINT 'AL is below or equal to 5' exit: RET

JNB

Short Jump if first operand is Not Below second operand (as set by CMP instruction). Unsigned.


Labeladdress

if CF = 0 then jump

include 'emu8086.inc' ORG 100h MOV AL, 7 CMP AL, 5 JNB label1 PRINT 'AL < 5.' JMP exit label1: PRINT 'AL >= 5.' exit: RET

JNBE

Short Jump if first operand is Not Below and Not Equal to second operand (as set by CMP instruction). Unsigned.


Labeladdress

if (CF = 0) and (ZF = 0) then jump

include 'emu8086.inc' ORG 100h MOV AL, 7 CMP AL, 5 JNBE label1 PRINT 'AL <= 5.' JMP exit label1: PRINT 'AL > 5.' exit: RET

JG

Short Jump if first operand is Greater then second operand (as set by CMP instruction). Signed.


Labeladdress

if (ZF = 0) and (SF = OF) then jump

include 'emu8086.inc' ORG 100h MOV AL, 5 CMP AL, -5 JG label1 PRINT 'AL is not greater -5.' JMP exit label1: PRINT 'AL is greater -5.' exit: RET

JGE

Short Jump if first operand is Greater or Equal to second operand (as set by CMP instruction). Signed.


Labeladdress

if SF = OF then jump

include 'emu8086.inc' ORG 100h MOV AL, 2 CMP AL, -5 JGE label1 PRINT 'AL < -5' JMP exit label1: PRINT 'AL >= -5' exit: RET

JNG

Short Jump if first operand is Not Greater then second operand (as set by CMP instruction). Signed.


Labeladdress

if (ZF = 1) and (SF <> OF) then jump

include 'emu8086.inc' ORG 100h MOV AL, 2 CMP AL, 3 JNG label1 PRINT 'AL > 3.' JMP exit label1: PRINT 'Al <= 3.' exit: RET

JNGE

Short Jump if first operand is Not Greater and Not Equal to second operand (as set by CMP instruction) Signed.


Labeladdress

if SF <> OF then jump

include 'emu8086.inc' ORG 100h MOV AL, 2 CMP AL, 3 JNGE label1 PRINT 'AL >= 3.' JMP exit label1: PRINT 'Al < 3.' exit: RET

JL

Short Jump if first operand is Less then second operand (as set by CMP instruction). Signed.


Labeladdress

if SF <> OF then jump

include 'emu8086.inc' ORG 100h MOV AL, -2 CMP AL, 5 JL label1 PRINT 'AL >= 5.' JMP exit label1: PRINT 'AL < 5.' exit: RET

JLE

Short Jump if first operand is Less or Equal to second operand (as set by CMP instruction). Signed.


Labeladdress

if SF <> OF or ZF = 1 then jump

include 'emu8086.inc' ORG 100h MOV AL, -2 CMP AL, 5 JLE label1 PRINT 'AL > 5.' JMP exit label1: PRINT 'AL <= 5.' exit: RET

JNL

Short Jump if first operand is Not Less then second operand (as set by CMP instruction). Signed.


Labeladdress

if SF = OF then jump

include 'emu8086.inc' ORG 100h MOV AL, 2 CMP AL, -3 JNL label1 PRINT 'AL < -3.' JMP exit label1: PRINT 'Al >= -3.' exit: RET

JNLE

Short Jump if first operand is Not Less and Not Equal to second operand (as set by CMP instruction)Signed.


Labeladdress

if (SF = OF) and (ZF = 0) then jump

include 'emu8086.inc' ORG 100h MOV AL, 2 CMP AL, -3 JNLE label1 PRINT 'AL <= -3.' JMP exit label1: PRINT 'Al > -3.' exit: RET


Labeladdress

Assembly Language Programming Part 2

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